Double patterning process

ABSTRACT

Double patterns are formed by coating a first chemically amplified positive resist composition comprising an acid labile group-bearing resin and a photoacid generator and prebaking to form a resist film on a processable substrate, exposing the resist film to high-energy radiation, PEB, and developing with an alkaline developer to form a first positive resist pattern, treating the first resist pattern to be alkali soluble and solvent resistant, coating a second resist composition and prebaking to form a reversal film, and exposing the reversal film to high-energy radiation, PEB, and developing with an alkaline developer to form a second positive resist pattern. The last development step includes dissolving away the reversed first resist pattern and achieving reversal transfer.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2008-032668 filed in Japan on Feb. 14, 2008,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a double patterning process for forming afirst pattern of reversal transfer and a second positive patternsimultaneously in an overlapping manner, involving the steps of forminga positive pattern through exposure and development, and heat orotherwise treatment for converting the positive pattern to be alkalisoluble, coating a second positive resist composition as a reversalfilm-forming composition thereon, and forming a second positive patternthrough exposure, bake and development, wherein the first pattern whichhas been converted to be alkali soluble can be removed at the same timeas the last development.

BACKGROUND ART

In the recent drive for higher integration and operating speeds in LSIdevices, the pattern rule is made drastically finer. Thephotolithography which is currently on widespread use in the art isapproaching the essential limit of resolution determined by thewavelength of a light source. As the light source used in thelithography for resist pattern formation, g-line (436 nm) or i-line (365nm) from a mercury lamp was widely used in 1980's. Reducing thewavelength of exposure light was believed effective as the means forfurther reducing the feature size. For the mass production process of 64MB dynamic random access memories (DRAM, processing feature size 0.25 μmor less) in 1990's and later ones, the exposure light source of i-line(365 nm) was replaced by a KrF excimer laser having a shorter wavelengthof 248 nm. However, for the fabrication of DRAM with a degree ofintegration of 256 MB and 1 GB or more requiring a finer patterningtechnology (processing feature size 0.2 μm or less), a shorterwavelength light source was required. Over a decade, photolithographyusing ArF excimer laser light (193 nm) has been under activeinvestigation. It was expected at the initial that the ArF lithographywould be applied to the fabrication of 180-nm node devices. However, theKrF excimer lithography survived to the mass-scale fabrication of 130-nmnode devices. So, the full application of ArF lithography started fromthe 90-nm node. The ArF lithography combined with a lens having anincreased numerical aperture (NA) of 0.9 is considered to comply with65-nm node devices. For the next 45-nm node devices which required anadvancement to reduce the wavelength of exposure light, the F₂lithography of 157 nm wavelength became a candidate. However, for thereasons that the projection lens uses a large amount of expensive CaF₂single crystal, the scanner thus becomes expensive, hard pellicles areintroduced due to the extremely low durability of soft pellicles, theoptical system must be accordingly altered, and the etch resistance ofresist is low; the postponement of F₂ lithography and the earlyintroduction of ArF immersion lithography were advocated (see Proc. SPIEVol. 4690 xxix).

In the ArF immersion lithography, the space between the projection lensand the wafer is filled with water. Since water has a refractive indexof 1.44 at 193 nm, pattern formation is possible even using a lenshaving a numerical aperture (NA) of 1.0 or greater. Theoretically, it ispossible to increase the NA to nearly 1.44. It was initially recognizedthat the resolution could be degraded and the focus be shifted by avariation of water's refractive index with a temperature change. Theproblem of refractive index variation could be solved by controlling thewater temperature within a tolerance of 1/100° C. while it wasrecognized that the impact of heat from the resist film upon lightexposure drew little concern. There was a likelihood that micro-bubblesin water could be transferred to the pattern. It was found that the riskof bubble generation is obviated by thorough deaeration of water and therisk of bubble generation from the resist film upon light exposure issubstantially nil. At the initial phase in 1980's of the immersionlithography, a method of immersing an overall stage in water wasproposed. Later proposed was a partial-fill method of using a waterfeed/drain nozzle for introducing water only between the projection lensand the wafer so as to comply with the operation of a high-speedscanner. In principle, the immersion technique using water enabled lensdesign to a NA of 1 or greater. In optical systems based on traditionalrefractive index materials, this leads to giant lenses, which woulddeform by their own weight. For the design of more compact lenses, acatadioptric system was proposed, accelerating the lens design to a NAof 1.0 or greater. A combination of a lens having NA of 1.2 or greaterwith strong resolution enhancement technology suggests a way to the45-nm node (see Proc. SPIE, Vol. 5040, p 724). Efforts have also beenmade to develop lenses of NA 1.35.

One candidate for the 32-nm node lithography is lithography usingextreme ultraviolet (EUV) radiation with wavelength 13.5 nm. The EUVlithography has many accumulative problems to be overcome, includingincreased laser output, increased sensitivity, increased resolution andminimized line-edge roughness (LWR) of resist coating, defect-free MoSilaminate mask, reduced aberration of reflection mirror, and the like.

The water immersion lithography using a NA 1.35 lens achieves anultimate resolution of 40 to 38 nm at the maximum NA, but cannot reach32 nm. Efforts have been made to develop higher refractive indexmaterials in order to further increase NA. It is the minimum refractiveindex among projection lens, liquid, and resist film that determines theNA limit of lenses. In the case of water immersion, the refractive indexof water is the lowest in comparison with the projection lens(refractive index 1.5 for synthetic quartz) and the resist film(refractive index 1.7 for prior art methacrylate-based film). Thus theNA of projection lens is determined by the refractive index of water.Recent efforts succeeded in developing a highly transparent liquidhaving a refractive index of 1.65. In this situation, the refractiveindex of projection lens made of synthetic quartz is the lowest,suggesting a need to develop a projection lens material with a higherrefractive index. LuAG (lutetium aluminum garnet Lu₃Al₅O₁₂) having arefractive index of at least 2 is the most promising material, but hasthe problems of birefringence and noticeable absorption. Even if aprojection lens material with a refractive index of 1.8 or greater isdeveloped, the liquid with a refractive index of 1.65 limits the NA to1.55 at most, failing in resolution of 32 nm despite successfulresolution of 35 nm. For resolution of 32 nm, a liquid with a refractiveindex of 1.8 or greater and resist and protective films with arefractive index of 1.8 or greater are necessary. Among the materialswith a refractive index of 1.8 or greater, the high refractive indexliquid seems least available. Such a liquid material has not beendiscovered because a tradeoff between absorption and refractive index isrecognized in the art. In the case of alkane compounds, bridged cycliccompounds are preferred to linear ones in order to increase therefractive index, but the cyclic compounds undesirably have too high aviscosity to follow high-speed scanning on the exposure tool stage. If aliquid with a refractive index of 1.8 is developed, then the componenthaving the lowest refractive index is the resist film, suggesting a needto increase the refractive index of a resist film to 1.8 or higher.

The process that now draws attention under the above-discussedcircumstances is a double patterning process involving a first set ofexposure and development to form a first pattern and a second set ofexposure and development to form a pattern between features of the firstpattern. See Proc. SPIE, Vol. 5754, p 1508 (2005). A number of doublepatterning processes are proposed. One exemplary process involves afirst set of exposure and development to form a photoresist patternhaving lines and spaces at intervals of 1:3, processing the underlyinglayer of hard mask by dry etching, applying another layer of hard maskthereon, a second set of exposure and development of a photoresist filmto form a line pattern in the spaces of the first exposure, andprocessing the hard mask by dry etching, thereby forming aline-and-space pattern at a half pitch of the first pattern. Analternative process involves a first set of exposure and development toform a photoresist pattern having spaces and lines at intervals of 1:3,processing the underlying layer of hard mask by dry etching, applying aphotoresist layer thereon, a second set of exposure and development toform a second space pattern on the remaining hard mask portion, andprocessing the hard mask by dry etching.

In either process, the hard mask is processed by two dry etchings. Boththe former and latter processes require two etchings for substrateprocessing, leaving the issues of a reduced throughput and deformationand misregistration of the pattern by two etchings.

One method that proceeds with a single etching is by using a negativeresist material in a first exposure and a positive resist material in asecond exposure. Another method is by using a positive resist materialin a first exposure and a negative resist material in a higher alcoholof 4 or more carbon atoms, in which the positive resist material is notdissolvable, in a second exposure. Since negative resist materials withlow resolution are used, these methods entail degradation of resolution.

A method which does not involve post-exposure bake (PEB) and developmentbetween first and second exposures is the simplest method with highthroughputs. This method involves first exposure, replacement by a maskhaving a shifted pattern drawn, second exposure, PEB, development anddry etching. However, the energy of light for second exposure offsetsthe energy of light for first exposure so that the contrast becomeszero, leading to a failure of pattern formation. If an acid generatorcapable of two photon absorption or a contrast enhancement layer (CEL)is used to provide nonlinear acid generation, then the energy offset isrelatively reduced even when second exposure is performed at ahalf-pitch shifted position. Thus a pattern having a half pitchcorresponding to the shift can be formed, though at a low contrast. SeeJpn. J. Appl. Phy. Vol. 33 (1994) p 6874-6877, Part 1, No. 12B, December1994. In this regard, if the mask is replaced on every exposure, thethroughput is substantially reduced. Then first exposure is performed ona certain number of wafers before second exposure is performed. Due toacid diffusion during the standing time between the first and secondexposures, there can occur dimensional variations which are of concern.

In addition to the double patterning technique, the technology forforming a fine space pattern or hole pattern includes use of negativeresist, thermal flow, and RELACS. The negative resist material suffersfrom the problem that the resist itself has a low resolution asdiscussed above. The thermal flow is another process of forming a finespace pattern. The space pattern once formed is heated at a temperatureabove the glass transition temperature (Tg) of the resist pattern,causing the pattern to flow to narrow the spaces. The RELACS known as afurther process of forming a fine space pattern is by applying on thespace pattern a composition in a solvent in which the resist pattern isnot soluble and adding chemical attachment by heat, thereby narrowingthe space.

The method of forming a negative pattern by reversal of a positivepattern is well known from the past. For example, JP-A 2-154266 and JP-A6-27654 disclose naphthoquinone resists capable of pattern reversal.JP-A 64-7525 describes exposure of selected portions of a film tofocused ion beam (FIB) for curing and flood exposure whereby the curedportions are left behind. JP-A 1-191423 and JP-A 1-92741 describeexposure of a photosensitive agent of naphthoquinone diazide to form anindene carboxylic acid, heat treatment in the presence of a base into anindene which is alkali insoluble, and flood exposure to effectpositive/negative reversal.

As to the positive/negative reversal method including exchange ofdevelopers, attempts were made to form negative patterns by developmentin an organic solvent of hydroxystyrene partially protected withtert-butoxycarbonyl (t-BOC) groups, and by development withsuper-critical carbon dioxide.

As to the positive/negative reversal method utilizing silicon-containingmaterials, it is proposed to form a fine hole pattern by covering aspace portion of a positive resist pattern with a silicon-containingfilm, effecting oxygen gas etching for etching away the positive patternportion, thus achieving positive/negative reversal to leave asilicon-containing film pattern. See JP-A 2001-92154 and JP-A2005-43420.

All the foregoing methods based on positive/negative reversal areimpractical due to process complexity and fail to form a fine pattern byfurther processing a pattern reversed film.

SUMMARY OF INVENTION Technical Problem

In connection with the fabrication of LSIs which are advancing towardhigher integration and operating speeds, double patterning is proposedand reported as being able to process to a very fine pattern rule.However, the process is not simple, and is regarded rather complex asrequiring first lithography, subsequent etching, second lithography, andfurther etching (2nd lithography and 2nd etching). There is a desire tohave a technique capable of processing by a single etching afterpatterning by two lithography processes. However, the technique ofconverting the first pattern to be insoluble in an organic solvent usedin the second resist composition, and improvements in the resolvingperformance of both the first and second resist compositions remain asimportant problems to be solved.

In addition to the double patterning technique, the technology forforming fine spaces is very important and includes use of negativeresist, thermal flow, and RELACS. The negative resist material suffersfrom the problem that the resist itself has a low resolution. Thethermal flow is another process of forming a fine space pattern. Becausethe quantity of pattern material available for flow is reduced as thefeature size becomes finer, the thermal flow process becomes difficultto reserve a sufficient quantity of flow. In general, resistcompositions capable of high resolution performance have a high glasstransition temperature (Tg) so that a sufficient flow may not occurduring the thermal flow step at a certain heating temperature. It isalso said that the size reduction by thermal flow encounters a limit.The RELACS known as a further process of forming a fine space pattern isby adding chemical attachment to the space pattern by heat, therebynarrowing the space. There are problems that the amount of attachmentvaries depending on the type of resist composition of which spaces areformed, and variations occur during dimensional shrinkage by heat.Another potential problem is a likelihood of generating pattern defects.

In connection with the fabrication of LSIs which are advancing towardhigher integration and operating speeds, there is a structure layerwhich requires a very fine pattern rule, especially fine space pattern.However, improving the miniaturization of only a space pattern isinsufficient. Because in the same layer, there may be present anisolated line and a pattern having different pitch or differentline/space ratio (duty ratio), the techniques for miniaturizing bothspaces and isolated lines must be compatible. Since the factor forenhancing the resolution of spaces is utterly different from the factorfor improving the resolution of isolated lines, the techniques forminiaturizing spaces and isolated lines are generally in tradeoffrelationship as well as the improvement in process margin. Solving theminiaturization of spaces and isolated lines at the same time becomesmore difficult as high-density integration and high-speed operation areaccelerated.

On the other hand, if a positive pattern once formed at a highresolution can be reversed to be negative, a fine space pattern isobtainable. As mentioned above, a variety of methods for reversing apositive image formed of a positive resist material capable of highresolution into a negative pattern have been reported. All these methodsbased on positive/negative reversal are impractical due to processcomplexity. They fail to form a fine pattern by further processing apattern reversed film. In the related art, only examples of reversaltransfer are known while there are no examples of double patterning inwhich lithographic patterning is applied to a film subject to reversaltransfer.

Solution to Problem

The inventors have found that when a resin in a first chemicallyamplified positive resist composition of which a positive resist patternis composed is subjected to partial crosslinking treatment, thecrosslinking reaction is controlled to proceed to such an extent toprovide the necessary organic solvent resistance and to keep asolubility in an alkaline developer; that when a reversal film is coatedthereon, a fine space pattern can be formed through positive/negativereversal by the treatment. Additionally, when the film to be coated forreversal transfer purpose is a positive resist film, the film materialto which the first resist pattern is reversal transferred can beprocessed by lithography. This enables double patterning.

Accordingly, in a first aspect, the invention provides a double patternforming process comprising the steps of:

coating a first chemically amplified positive resist composition onto aprocessable substrate, said resist composition comprising a resincomprising recurring units having an alkali-soluble group protected withan acid labile group which is eliminatable with acid, the resin beingconvertible to be soluble in an alkaline developer as a result ofelimination of acid labile groups, a photoacid generator capable ofgenerating an acid upon exposure to high-energy radiation, and anorganic solvent, and prebaking the resist composition to remove theunnecessary solvent to form a resist film,

exposing the resist film to high-energy radiation in a first pattern ofexposed and unexposed areas, post-exposure baking for causing the acidgenerated by the acid generator upon exposure to act on the acid labilegroups on the resin whereby the acid labile groups on the resin in theexposed area undergo elimination reaction so that the resin in theexposed area becomes alkali soluble, and developing the exposed resistfilm with an alkaline developer to form a first positive resist pattern,

treating the first resist pattern so as to eliminate the acid labilegroups on the resin in the first resist pattern and to inducecrosslinking in the resin to such an extent that the resin may not losea solubility in an alkaline developer, for thereby endowing the firstresist pattern with resistance to an organic solvent to be used in areversal film-forming composition,

coating a reversal film-forming composition thereon to form a reversalfilm, said reversal film-forming composition being a second chemicallyamplified positive resist composition comprising a resin comprisingrecurring units having an alkali-soluble group protected with an acidlabile group which is eliminatable with acid, a photoacid generatorcapable of generating an acid upon exposure to high-energy radiation,and an organic solvent, and prebaking the second resist composition toremove the unnecessary solvent to form the reversal film, and

exposing the reversal film to high-energy radiation in a second patternof exposed and unexposed areas, post-exposure baking for causing theacid generated by the acid generator upon exposure to act on the acidlabile groups on the resin whereby the acid labile groups on the resinin the exposed area undergo elimination reaction, and developing theexposed reversal film with an alkaline developer to form a secondpositive resist pattern,

wherein the last step of developing the exposed reversal film with analkaline developer to form a second resist pattern includes dissolvingaway the first resist pattern which has been converted to be soluble inthe alkaline developer and achieving reversal transfer of the firstresist pattern to the second resist pattern.

The inventors have found that partial crosslinking between molecules ofthe resin of which the positive pattern of the first resist film iscomposed has a level that maintains a solubility in an alkalinedeveloper resulting from elimination of acid labile groups and providesresistance to an organic solvent at the same time. This permits removalof the positive pattern portion in the final step of positive/negativereversal to be implemented in a very simple manner. Additionally, thefilm subject to reversal transfer is made of a chemically amplifiedpositive resist composition which can be processed by lithography. Thisenables double patterning.

In a preferred embodiment, in the step of exposing, baking anddeveloping to form a second resist pattern, exposure to the secondpattern is performed between features of the first pattern to define thesecond resist pattern of spaces which are removable by alkalinedevelopment and located between spaces in the pattern resulting fromreversal transfer of the first resist pattern, whereby repetitivepatterns of lines and spaces are formed on the processable substrate.

Then, fine lines and spaces can be formed (or patterned) on theprocessable substrate by two lithography steps. Since this need befollowed by a single etching only, a simplified double patterningprocess is provided.

In a preferred embodiment, in the step of exposing, baking anddeveloping to form a second resist pattern, exposure to the secondpattern is performed at a position spaced apart from the first resistpattern, whereby the second resist pattern is formed on the processablesubstrate apart from the pattern resulting from reversal transfer of thefirst resist pattern.

This embodiment also provides a simplified double patterning processinvolving two lithographic steps to form patterns on the processablesubstrate and subsequent single etching. In the single patterningprocess (involving a single exposure step for patterning), improving theprocess margins of a fine space pattern, and a pattern having anisolated line or different pitch or different line/space ratio (dutyratio) is believed quite difficult because of their tradeoffrelationship. The double patterning process of the invention enables toimprove both the process margins. That is, the reversed first resistpattern enables resolution of fine spaces, and a pattern having mixedisolated lines or different pitch or different line/space ratio (dutyratio) can be formed from the second positive resist composition. Thisleads to the advantage of improving the process margins of both thepatterns.

The double patterning process of the invention enables to form a varietyof patterns by reducing the pitch between pattern features, or by twoexposure steps of intersecting patterns and positive/negative reversalof the first pattern. For example, a crisscross hole pattern and apattern of holes with very thin walls therebetween can be formed inpreferred embodiments.

In a preferred embodiment for implementing the step of forming a firstresist pattern, the first chemically amplified positive resistcomposition comprises a resin comprising recurring units having alactone ring and recurring units of alicyclic structure having analkali-soluble group protected with an acid labile group which iseliminatable with acid. While the lactone ring structure is known toimpart adhesion to the resist film, the resin comprising such units isadvantageously used in crosslink formation in the step of endowing theresin with organic solvent resistance.

In a preferred embodiment, the first chemically amplified positiveresist composition comprises a resin comprising recurring units having a7-oxanorbornane ring and recurring units having an alkali-soluble groupprotected with an acid labile group of alicyclic structure which iseliminatable with acid, and the step of treating the first resistpattern so as to eliminate the acid labile groups on the resin in thefirst resist pattern is performed by heating whereby elimination of acidlabile groups and crosslinking of the resin simultaneously take place.The 7-oxanorbornane ring advantageously serves to impart organic solventresistance.

In a preferred embodiment, the recurring units having a 7-oxanorbornanering are recurring units having the general formula (a).

Herein R¹ is hydrogen or methyl, R² is a single bond or a straight,branched or cyclic C₁-C₆ alkylene group which may have an ether or estergroup, and which has a primary or secondary carbon atom through which itis linked to the ester moiety in the formula, R³, R⁴ and R⁵ are eachindependently hydrogen or a straight, branched or cyclic C₁-C₆ alkylgroup, and “a” is a number in the range: 0<a<1.0.

In a preferred embodiment, the recurring units having an alkali-solublegroup protected with an acid labile group which is eliminatable withacid are recurring units having the general formula (b):

Herein R⁶ is hydrogen or methyl, R⁷ is an acid labile group, and b is anumber in the range: 0<b≦0.8. The inclusion of units of the illustratedstructure ensures that the dissolution rate is readily increased byreaction with acid, improving the resolution performance of the firstresist film and facilitating removal with the alkaline developer of thesecond resist film serving as the film subject to reversal transfer.

In a preferred embodiment, the second chemically amplified positiveresist composition comprises a resin comprising recurring units having alactone ring and recurring units having an alkali-soluble groupprotected with an acid labile group which is eliminatable with acid. Thelactone ring structure functions to impart adhesion to the second resistfilm as in the case of the first resist film.

In a preferred embodiment of the second chemically amplified positiveresist composition, the recurring units having an alkali-soluble groupprotected with an acid labile group which is eliminatable with acid arerecurring units having the general formula (c).

Herein R⁸ is hydrogen or methyl, R⁹ is an acid labile group, and c is anumber in the range: 0<c≦0.8.

In a preferred embodiment of the second chemically amplified positiveresist composition, the resin comprising recurring units having analkali-soluble group protected with an acid labile group which iseliminatable with acid is a polysiloxane compound.

In a preferred embodiment, the polysiloxane compound comprisesstructural units having the general formulae (1) and (2) and furthercomprises third structural units having the general formula (3).

Herein R¹⁰ is a C₃-C₂₀ monovalent organic group of straight, branched,cyclic or polycyclic structure which has a hydroxyl group on a carbonatom as a functional group, which has in total at least three fluorineatoms substituted on the carbon atoms bonded to the hydroxyl-bondedcarbon atom, and which may contain a halogen, oxygen or sulfur atom inaddition to the fluorine atoms; R¹¹ is a C₁-C₆ monovalent hydrocarbongroup of straight, branched or cyclic structure; R¹² is a C₃-C₂₀monovalent organic group of straight, branched, cyclic or polycyclicstructure which has a carboxyl group protected with an acid labileprotective group as a functional group, and which may contain a halogen,oxygen or sulfur atom in addition to the carboxyl group; R¹³ is asdefined for R¹¹; R¹⁴ is a C₄-C₁₆ monovalent organic group which has alactone ring as a functional group and which may contain a halogen,oxygen or sulfur atom in addition to the lactone ring; R¹⁵ is as definedfor R¹¹; p is 0 or 1, q is 0 or 1, and r is 0 or 1.

In a preferred embodiment, the step of treating the first resist patternfor endowing the first resist pattern with resistance to an organicsolvent to be used in a reversal film-forming composition includesheating at a higher temperature than in the prebaking and PEB steps.

Typically, ArF immersion lithography is used in the pattern formingprocess of the invention. In the ArF immersion lithography, water isgenerally used as the liquid, and it is a common practice to use aprotective coating for preventing the acid from being leached out inwater.

A pattern forming process using a protective coating is alsocontemplated herein. A further embodiment of the invention is a doublepattern forming process comprising the steps of:

coating a first chemically amplified positive resist composition onto aprocessable substrate, said resist composition comprising a resincomprising recurring units of the structure having an alkali-solublegroup protected with an acid labile group which is eliminatable withacid, the resin being convertible to be soluble in an alkaline developeras a result of elimination of acid labile groups, a photoacid generatorcapable of generating an acid upon exposure to high-energy radiation,and an organic solvent, and prebaking the resist composition to removethe unnecessary solvent to form a resist film,

coating a protective film-forming composition onto the resist film andheating to remove an unnecessary solvent to form a protective film,

exposing the resist film to high-energy radiation in a first pattern ofexposed and unexposed areas, post-exposure baking for causing the acidgenerated by the acid generator upon exposure to act on the acid labilegroups on the resin whereby the acid labile groups on the resin in theexposed area undergo elimination reaction so that the resin in theexposed area becomes alkali soluble, and developing the exposed resistfilm with an alkaline developer to form a first positive resist pattern,

treating the first resist pattern so as to eliminate the acid labilegroups on the resin in the first resist pattern and to inducecrosslinking in the resin to such an extent that the resin may not losea solubility in an alkaline developer, for thereby endowing the firstresist pattern with resistance to an organic solvent to be used in areversal film-forming composition,

coating a reversal film-forming composition thereon to form a reversalfilm, said reversal film-forming composition being a second chemicallyamplified positive resist composition comprising a resin comprisingrecurring units of the structure having an alkali-soluble groupprotected with an acid labile group which is eliminatable with acid, aphotoacid generator capable of generating an acid upon exposure tohigh-energy radiation, and an organic solvent, and prebaking the secondresist composition to remove the unnecessary solvent to form thereversal film,

coating a protective film-forming composition onto the reversal film andheating to remove an unnecessary solvent to form a protective film, and

exposing the reversal film to high-energy radiation in a second patternof exposed and unexposed areas, post-exposure baking for causing theacid generated by the acid generator upon exposure to act on the acidlabile groups on the resin whereby the acid labile groups on the resinin the exposed area undergo elimination reaction, and developing theexposed reversal film with an alkaline developer to form a secondpositive resist pattern,

wherein the last step of developing the exposed reversal film with analkaline developer to form a second resist pattern includes dissolvingaway the first resist pattern which has been converted to be soluble inthe alkaline developer and achieving reversal transfer of the firstresist pattern to the second resist pattern, thereby forming a patternresulting from reversal transfer of the first resist pattern and thesecond resist pattern.

Advantageous Effects of Invention

According to the invention, a second positive resist composition servingas the reversal film-forming composition is coated onto the firstpositive resist pattern. Even when a second resist film serving as thereversal film is formed by coating the second positive resistcomposition in solution form in a hydroxyl-containing solvent or ahighly polar solvent such as an ester or ketone, the second resistcomposition serving as the reversal film-forming material can be buriedin gaps in the first positive resist pattern without causing damage tothe first positive resist pattern. In addition, the positive patternmade of the first positive resist composition can be dissolved away inan alkaline developer. Thus positive/negative reversal can be carriedout at a high accuracy through simple steps.

Image reversal from a positive pattern to a negative pattern by thismethod ensures that using a first fine line pattern, a fine spacepattern of the same size can be reversal-formed. In the case of a trenchpattern, a line pattern having a capability to form a finer feature sizeis formed through exposure, and this is converted into a trench patternby the image reversal technology described above, whereby an ultra-finetrench pattern can be formed.

This positive/negative reversal method may be advantageously utilized inthe following case. An overdose of exposure permits a finer size patternto be formed from a positive pattern. While it is technically verydifficult to form isolated spaces (trench pattern) below the exposurethreshold, an ultra-fine trench pattern can be formed by first formingpositive pattern lines thinner than the ordinary exposure thresholdusing an overdose of exposure and then reversing the pattern accordingto the method of the invention.

In this way, double patterning is enabled by transferring fine lines ofthe first resist to the second resist through positive/negativereversal, thereby forming an ultra-fine space pattern and subjecting thesecond resist to resolution.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates in cross-sectional view the patternforming process of the invention, state (A) that a processable substrateand a first resist film are disposed on a substrate.

FIG. 2 schematically illustrates in cross-sectional view the patternforming process of the invention, state (B) that the first resist filmis exposed and developed.

FIG. 3 schematically illustrates in cross-sectional view the patternforming process of the invention, the developed state (B-1) that linesof thinner size are finished in the resist film by over-exposure.

FIG. 4 schematically illustrates in cross-sectional view the patternforming process of the invention, state (C) that the resist pattern isdeprotected and crosslinked under the action of acid and heat.

FIG. 5 schematically illustrates in cross-sectional view the patternforming process of the invention, state (D) that a pattern reversal filmis coated.

FIG. 6 schematically illustrates in cross-sectional view the patternforming process of the invention, state (D-1) that the first resistpattern has an increased height and a coating of the second resist has areduced thickness, so that the first resist pattern converted to besoluble in alkaline developer is exposed to an alkaline developer.

FIG. 7 schematically illustrates in cross-sectional view the patternforming process of the invention, state (E) that the reversed firstresist is removed with an alkaline developer without patterning thesecond resist serving as a film subject to reversal transfer.

FIG. 8 schematically illustrates in cross-sectional view the patternforming process of the invention, state (F-1) that exposure is made suchthat spaces of the second resist are formed between features of thereversed first resist pattern.

FIG. 9 schematically illustrates in cross-sectional view the patternforming process of the invention, the double pattern formed state (F-2)that the first resist pattern which has been converted to be soluble inalkaline developer and the second resist film which has been exposed soas to form a space pattern between features of the first resist patternare removed with an alkaline developer.

FIG. 10 schematically illustrates in cross-sectional view the patternforming process of the invention, state (F-3) that exposure of the firstresist film is performed at a position spaced apart from the firstresist pattern to be reversed into spaces.

FIG. 11 schematically illustrates in cross-sectional view the patternforming process of the invention, the double pattern formed state (F-4)state that the first resist pattern which has been converted to besoluble in alkaline developer and an isolated line pattern at a positionspaced apart from the first resist pattern to be reversed are formed.

FIG. 12 is a plan view illustrating the pattern forming process of theinvention, state (G-1) that on five Y-direction lines of the firstpattern which result from the resist pattern being deprotected andcrosslinked under the action of acid and heat, a second resist film iscoated and exposed to a second pattern in the form of a cutout patternextending perpendicular to the first pattern.

FIG. 13 is a plan view illustrating the pattern forming process of theinvention, state (G-2) that the first pattern is positive/negativereversed by development and spaces of the second pattern are resolved atthe same time.

FIG. 14 is a plan view illustrating the pattern forming process of theinvention, state (H-1) that on five Y-direction lines of the firstpattern which result from the resist pattern being deprotected andcrosslinked under the action of acid and heat, a second resist film iscoated and exposed to a second pattern to leave five X-direction linesextending perpendicular to the first pattern.

FIG. 15 is a plan view illustrating the pattern forming process of theinvention, state (H-2) that the first pattern is positive/negativereversed by development and lines of the second pattern are interruptedby reversal of the first pattern at the same time whereby a fine dotpattern is resolved.

FIG. 16 is a plan view illustrating the pattern forming process of theinvention, state (I-1) showing double (double dipole) exposures of X andY lines.

FIG. 17 is a plan view illustrating the pattern forming process of theinvention, state (I-2) that a dot pattern is formed in the first resistfilm by development and the first resist pattern is deprotected andcrosslinked under the action of acid and heat.

FIG. 18 is a plan view illustrating the pattern forming process of theinvention, state (I-3) that a second resist is coated, exposed to apattern of holes disposed between dots of the first resist, anddeveloped so that a hole pattern is formed through positive/negativereversal of the first resist pattern and a hole pattern of the secondresist pattern is formed at the same time.

FIG. 19 schematically illustrates a resist pattern obtained in Examples43 and 44.

FIG. 20 schematically illustrates a resist pattern in ComparativeExample 9.

FIG. 21 schematically illustrates a resist pattern in Example 45.

FIG. 22 schematically illustrates a resist pattern in ComparativeExample 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The terms “a” and “an” herein do not denote a limitation of quantity,but rather denote the presence of at least one of the referenced item.As used herein, the notation (C_(n)-C_(m)) means a group containing fromn to m carbon atoms per group. The abbreviation “phr” refers to parts byweight per 100 parts by weight of resin. The terms “converted” and“reversed” are used interchangeably in the context that resist film isconverted from an alkali-insoluble state to an alkali-soluble state, andthe same applies to the term “reversal.”

There were several problems to be overcome in the course of developmentworks. In the situation where a reversal film is formed on a once formedpositive pattern, how to deposit a new coating without disrupting theunderlying pattern is one of such problems. Our initial approach to thisproblem is to form a reversal film after a positive pattern iscrosslinked and insolubilized in a solvent.

In the invention, a film subject to reversal transfer is a second resistfilm so that double patterns may be formed. The inventors have foundthat insolubilization of the first pattern in a solvent used in coatingof the second resist composition for forming a reversal film isimplemented by utilizing crosslinking of the first pattern. It ispreferred that this crosslinking reaction is performed by the existingtechnique or in the existing equipment in the current semiconductordevice fabrication system, especially based on lithography. For example,it is believed unfavorable to introduce a high-energy radiationirradiating step capable of photo-reaction to facilitate crosslinkingreaction because of a negative impact on productivity. It is alsobelieved unfavorable to build a special expensive processing unit suchas a high-energy radiation irradiating unit in the system.

It is desired that crosslinking of the pattern of first resist film toacquire resistance to an organic solvent used in the second resist filmserving as the reversal film be accomplished only by high-temperaturebaking. If possible only by high-temperature baking, the inventionachieves outstanding practical effects because high-temperature hotplates are commonly used in the semiconductor device fabrication system.

It is also required that crosslinking of the pattern of first resistfilm to acquire resistance to an organic solvent used in the secondresist film serving as the reversal film do not detract from a highsolubility in an alkaline developer for the second resist film essentialfor removing the second resist pattern.

Making studies on the composition of a first chemically amplifiedpositive resist material and the treating conditions thereof so as toinduce thermal crosslinkage to impart resistance to an organic solventused in the second resist film serving as the reversal film, theinventors have reached the present invention.

Another problem to be overcome is how to selectively remove the firstpositive pattern relative to the reversal film. Like the equipmentreferred to above, the means of removing the first pattern also existsin the current semiconductor fabrication system. In particular, it ispreferred to remove the first pattern by the existing technique or unitused in the lithography system. It would be desirable to effect removalsimply with an alkaline developer. Dry etching may also be used, withthe disadvantages of process complexity and a lower throughput. It isdesired to remove the first pattern by means of an alkaline developmentunit existing in the lithography system and transfer its image to asecond pattern if possible.

It has been found that the pattern of unexposed areas in the firstpositive resist film is, of course, insoluble in an alkaline developerbecause alkali-soluble groups are kept protected with acid labile groupswhich are eliminatable with acid, and that when heated, a minor amountof acid which has diffused from exposed areas and remains in the patternreacts with acid labile groups at high temperature to eliminate the acidlabile groups so that the pattern of first positive resist film becomesalkali soluble. It has also been found that some acid labile groups arethermally eliminated by heating at high temperature. It is confirmedthat by heating at high temperature, the first resist pattern isconverted from the alkaline developer-insoluble positive behavior to analkaline developer-soluble behavior. The reversal of the positivepattern of first resist film to alkaline solubility means that the firstresist film can be readily removed together with the second resist filmsubject to reversal transfer, using an alkaline developer. The reversedfirst resist pattern can be removed more readily than the second resistfilm during the alkaline development step of patterning the secondresist film, achieving a high efficiency.

Making studies on a first resist composition and treating conditionsthereof so as to induce crosslinking reaction in the first resistpattern to enhance resistance to an organic solvent used in coating of asecond resist film subject to reversal transfer while maintaining alkalisolubility of the reversed first resist pattern, the inventors haveestablished a double pattern forming process involving reversal transferof the first positive resist film to the second resist film andpatterning of the second resist film.

Besides the problems to be overcome, there are several issues which mustbe taken into account in the practice of the invention.

A first issue relates to the thickness of a first resist film and asecond resist film. To remove the first resist pattern which has beenconverted to be alkali soluble from the second resist film duringalkaline development, the top of the first resist pattern must beexposed over the upper surface of the second resist film becauseotherwise the first resist pattern is not contacted with the alkalinedeveloper or removed. Accordingly, it must be considered that the heightof the first resist film pattern is increased and the coating thicknessof the second resist film is reduced. However, it is generally believedfavorable that the second resist film overlies and covers the firstresist pattern because otherwise the height (aspect ratio=height/size ofline pattern) of the second resist pattern becomes lower and due toprocess management. Coverage of the first resist pattern with the secondresist film ensures that the second resist film is buried close betweenfeatures of the first resist pattern. Coverage of the first resistpattern with the second resist film, however, prevents the reversedfirst resist pattern from being removed by alkaline development. Thusthe second resist film is designed to have some solubility in analkaline developer so that the second resist film is somewhat slimmed(reduced in thickness) with the alkaline developer to provide access toalkali-soluble portions of the first resist pattern by the alkalinedeveloper, allowing the developer to contact the first resist pattern.

As described just above, the second resist film to which the firstresist pattern is reversal transferred is designed to have such asolubility in an alkaline developer that the alkaline developer may gainaccess to the first resist film.

However, it must be borne in mind that the film to which the firstresist pattern is transferred is the second resist film to be patterned.The provision of the second resist film with a rate of dissolution in analkaline developer may lead to degradation of the dissolution contrastof the second resist film that governs its resolution performance. This,in turn, leads to a likelihood of degrading the patterning performanceof the second resist film and degrading process margins such as adecline of bridge margin. In particular, substantial slimming duringpatterning of the second resist film is not preferable because theresist pattern loss that the height of finished resist pattern isreduced becomes noticeable, and a degradation of profile resulting frompattern edge chipping is observed.

Continuing research works, the inventors have made the followingdiscovery. Even when the first resist pattern is completely overlaidwith the second resist film, the inventors have succeeded in removingthe reversed first resist film from the second resist film by analkaline developer, thereby transferring the reversed first resistpattern to the second resist film, without a need to provide the secondresist film with a certain rate of dissolution in an alkaline developerso that the alkaline developer may gain access to the first resist film.More specifically, some acid which has diffused from exposed areas andremains in the first resist pattern or the acid generated by thermaldecomposition of the photoacid generator in the resist compositionremaining in the first resist pattern during the step of heating at hightemperature for endowing the first resist pattern with resistance tosolvent for the second resist film while maintaining a solubility inalkaline developer of the first resist pattern, acts on alkali-solublegroups protected with acid labile groups which are eliminatable withacid in the second resist film overlying the first resist pattern,whereby acid elimination occurs in the baking steps of a processinvolving coating, prebaking, exposure and post-exposure baking thesecond resist film. The second resist film overlying the first resistpattern is then converted to be alkali soluble. Then, during thedevelopment step for patterning the second resist film, the secondresist film overlying the first resist pattern is dissolved away and thereversed first resist pattern is also removed.

As described above, it has been found that the reversed first resistpattern can be removed from the second resist film without a need toprovide the second resist film with a certain rate of dissolution inalkaline developer. Of course, if the thickness of the second resistfilm coated is extremely thick, or if the second resist film overlyingthe first resist pattern is extremely thick, then the acid originatingfrom the first resist pattern and migrating outward does not fullypermeate into the second resist film containing acid labile groups whichare eliminatable with acid, thus failing to convert the second resistfilm overlying the first resist pattern to be alkali soluble andrestraining the alkaline developer from reaching the reversed firstresist pattern. This leads to a failure in removal of the reversed firstresist pattern and in reversal transfer of the first resist pattern tothe second resist film. It is then absolutely essential that thethickness of the second resist film be thinner than the thickness of thefirst resist film, provided that the thickness is measured as coated ona flat substrate. In an example where the first resist film is coated toa thickness of 1,200 Å on a flat substrate, if the second resist film iscoated to a thickness of 600 Å on a flat substrate, the second resistfilm is buried close between features of the first resist pattern andalso overlies the first resist pattern. Since the second resist filmoverlying the first resist film is converted to be alkali soluble underthe action of acid generated from the first resist pattern, theoverlying second resist film and the reversed first resist pattern aresimultaneously removed by an alkaline developer.

The height of the first resist pattern is also an importantconsideration. When the first resist film is coated and patterned, theresulting first resist pattern often suffers from a top loss, that is,becomes lower in height. In addition, the first resist pattern undergoesthermal shrinkage under the action of heat released in the step ofheating at high temperature the first resist pattern to inducecrosslinking reaction to enhance its resistance to solvent used incoating of the second resist film, and this thermal shrinkage must alsobe taken into account. Therefore, the height of the first resist patternprior to coating of the second resist film is important. The secondresist film must be buried in the first resist pattern beyond thatheight, and overlie the first resist pattern. In addition, the thicknessof a portion of the second resist film overlying the first resistpattern should be such that the acid originating from the first resistfilm may permeate into the second resist film to induce acid-assistedelimination of acid labile groups therein.

It is preferred, needless to say, that the height of the first resistpattern prior to coating of the second resist film be higher, and thefirst resist pattern experience a less top loss. The reason is that ifthe first resist film experiences a substantial top loss and its patternhas a reduced height, the second resist film overlying the first resistpattern becomes thin and so, the double patterns including thereversal-transferred first resist pattern and the second resist patternare finished to a reduced height (aspect ratio). The first resistcomposition must be formulated so that the first resist pattern subjectto reversal transfer may have a height.

With the height of the first resist film as patterned taken intoaccount, the preferred thicknesses of the first and second resist filmscoated are as follows. The thickness of the second resist film as coatedon a flat substrate is preferably 60% to 50% of the thickness of thefirst resist film as coated on a flat substrate. If their thicknessesare below the range, the double patterns including the pattern ofreversal transfer of the first resist film and the second resist patternfail to acquire a height.

As described above, some acid which has diffused from exposed areas andremains in the first resist pattern or the acid generated by thermaldecomposition of the photoacid generator in the resist compositionremaining in the first resist pattern during the step of heating at hightemperature for endowing the first resist pattern with resistance tosolvent for the second resist film while maintaining a solubility inalkaline developer of the first resist pattern acts on alkali-solublegroups protected with acid labile groups which are eliminatable withacid in the second resist film overlying the first resist pattern,whereby acid elimination occurs in the baking steps of a processinvolving coating, prebaking, exposure and post-exposure baking thesecond resist film. The second resist film overlying the first resistpattern is then converted to be alkali soluble. Then, during thedevelopment step for patterning the second resist film, the secondresist film overlying the first resist pattern is dissolved away and thereversed first resist pattern is also removed simultaneously. Inconnection with this finding, positive addition to the first resistcomposition of a thermal acid generator capable of generating acid underthe action of heat was devised for the purpose of making up for someacid which has diffused from exposed areas and remains in the firstresist pattern or the acid generated by thermal decomposition of thephotoacid generator in the resist composition remaining in the firstresist pattern during the step of heating at high temperature forendowing the first resist pattern with solvent resistance. Regrettably,it was found that excess thermal acid generator added to the firstresist film can adversely affect the resolution performance and processmargin of the first resist film when it is patterned. For example, thethermal acid generators are ammonium salts of acids. It is inferred thatan anion exchange occurs between the ammonium salt and an onium saltused as the photoacid generator within the resist material, failing toachieve the desired resolution capability. For example, a resistmaterial having a thermal acid generator added is observed as behavingto enhance the diffusion of acid acting on acid labile groups within theresist film. The enhanced acid diffusion exacerbates process margins ofa resist pattern to be formed such as exposure latitude and mask errorfactor (MEF). In addition, when a thermal acid generator is positivelyadded, it functions advantageously to assist the first resist film indeveloping alkali solubility and promoting crosslinking reaction toendow resistance to organic solvent used in coating of the second resistfilm. However, if excess acid is generated and remains in the firstresist film, it noticeably acts on acid labile groups in the secondresist film, giving rise to the problem that in transfer of the reversedfirst resist pattern, acid labile groups in the second resist filmserving as a transfer film change to be alkali soluble so that the sizeof the transferred pattern is enlarged. Moreover, if excess acid isgenerated and remains in the first resist pattern and diffusesnoticeably into the second resist film, then it may act on acid labilegroups throughout the second resist film. Then the overall second resistfilm is converted to be alkali soluble, failing to transfer the firstresist pattern. In addition to a failure to form a second resistpattern, the overall second resist film is removed. At worst no filmsmay be left behind.

It was also found that the addition of a thermal acid generator candeteriorate the thermal properties of the first resist film. The thermalacid generator added behaves as a plasticizer in the step of heating athigh temperature the first resist pattern to induce crosslinkage toendow it with resistance to solvent for the second resist film, givingrise to the problem that the first resist pattern undergoes thermal flowduring this heating step.

As discussed above, the addition of a thermal acid generator to thefirst resist composition is preferred in that it assists the firstresist film in developing alkaline solubility and promotes crosslinkingreaction to endow resistance to organic solvent used in coating of thesecond resist film, but excess addition gives rise to several problems.The thermal acid generator is added in such amounts as to avoid anysubstantial impacts on the lithography of patterning the first resistfilm, on the thermal properties of the first resist film, and on thesecond resist film. The amount of thermal acid generator added isgenerally up to 5%, preferably up to 3%, and more preferably 1 to 0.01%based on the weight of the base resin in the first resist composition.

While several issues to be considered in the practice of the inventionare discussed, attention must also be paid to the thermal properties ofthe first resist film and the temperature associated with the step ofheating at high temperature the first resist film to assist the firstresist film in developing alkaline solubility and to facilitatecrosslinking reaction to endow it with resistance to organic solventused in coating of the second resist film.

The temperature associated with the step of heating at high temperaturethe first resist film to assist the first resist film in developingalkaline solubility and to facilitate crosslinking reaction to endow itwith resistance to organic solvent used in coating of the second resistfilm should desirably be higher than the temperatures encountered in theprocess for patterning the first resist film involving coating,prebaking, exposure and post-exposure baking. If crosslinking reactionoccurs even at a temperature which is close to the temperatures ofprebaking and post-exposure baking in the first resist film patterningprocess, this leads to the risk that crosslinking reaction takes placeduring patterning of the first resist film, failing to avoid negativeimpacts on lithographic characteristics. It is undesirable thatcrosslinking reaction occur at a higher temperature than the glasstransition temperature (Tg) of the first resist pattern. The reason isthat if the first resist pattern is heated at a higher temperature thanits Tg, the first resist pattern undergoes thermal flow to enlarge thepattern size or to disable fine-size processing. If thermal flow occurs,the resist pattern is reduced in height, which is also undesirable.

The temperature associated with the step of heating at high temperaturethe first resist film to assist the first resist film in developingalkaline solubility and to facilitate crosslinking reaction to endow itwith resistance to organic solvent used in coating of the second resistfilm is preferably at least 150° C., and more preferably in the range of180 to 220° C. A photoacid generator and a basic compound in a resistmaterial generally serve as plasticizers to reduce the Tg of the resistpattern so that the thermal flow incipient temperature becomes lower.Since the photoacid generator and basic compound are essentialcomponents in the resist material, the Tg of resist base resin itselfmust be elevated depending on the addition and plasticizing effects ofthese components. Accordingly, the resist base resin has an optimum Tgof at least 150° C., and preferably at least 180° C. If the heatingtemperature to facilitate crosslinking reaction is above 220° C., anappropriate first resist pattern to be reversal-transferred to thesecond resist film cannot be formed due to substantial thermal shrinkageand thermal damages of the first resist film. As discussed above, anycrosslinking reaction hardly takes place when the heating temperature tofacilitate crosslinking reaction is below 150° C.

A further issue to be considered in the practice of the invention is arate of dissolution in alkaline developer of the first resist film whichhas been converted to be alkali soluble. As described above, a minoramount of acid which has diffused from exposed areas and remains in thepattern reacts with acid labile groups at high temperature to eliminatethe acid labile groups so that the first positive resist pattern becomesalkali soluble, and some acid labile groups are thermally eliminated byheating at high temperature. Thus, the first resist pattern can beconverted from the alkaline developer-insoluble positive behavior to thealkaline developer-soluble behavior by heating at high temperature. Anappropriate measure of dissolution rate is that the reversed firstresist pattern has a dissolution rate in excess of 2 nm/sec whendeveloped with a 2.38 wt % aqueous solution of tetramethylammoniumhydroxide (TMAH) commonly used in the alkaline development of resistfilms.

Making extensive investigations on the task of converting the firstpositive resist pattern to be alkali soluble, the task of endowing thefirst resist pattern with organic solvent resistance during coating ofthe second resist film serving as a reversal transfer film, and otherissues to be overcome in implementing the invention, the inventors havecompleted the double patterning process.

Now the invention is described in further detail.

The base resin in the first positive resist composition used in thepattern forming process is advantageously a polymer comprising recurringunits having a lactone ring, more specifically recurring units having a7-oxanorbornane ring, and preferably recurring units of the generalformula (a). These units are used as adhesive units. The process isadvantageously applicable with this polymer without adding a furthercomponent(s) to the base resin.

Herein R¹ is hydrogen or methyl, R² is a single bond or a straight,branched or cyclic C₁-C₆ alkylene group which may have an ether (—O—) orester (—COO—) group, and which has a primary or secondary carbon atomthrough which it is linked to the ester moiety in the formula, R³, R⁴,and R⁵ are each independently hydrogen or a straight, branched or cyclicC₁-C₆ alkyl group, and “a” is a number in the range: 0<a<1.0.

Examples of the C₁-C₆ alkylene group include methylene, ethylene,n-propylene, isopropylene, n-butylene, isobutylene, sec-butylene,n-pentylene, isopentylene, cyclopentylene, n-hexylene, andcyclohexylene.

Examples of the C₁-C₆ alkyl group include methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl, isopentyl,cyclopentyl, n-hexyl, and cyclohexyl.

The monomers from which recurring units of formula (a) are derived aremonomers Ma of the following formula wherein R¹ to R⁶ are as definedabove.

Examples of monomers Ma are shown below.

In the embodiment of the process, once a first resist pattern is formedthrough exposure and development, deprotection of acid labile groups andcrosslinking are brought about under the action of acid and heat. Asecond resist film serving as a reversal film is coated thereon,patterned and alkali developed. The first resist pattern is removed atthe same time as the last development, forming double patterns.

The acid contributing to crosslinking reaction may include the acidwhich has diffused from exposed areas and remains in the first resistpattern and the acid resulting from thermal decomposition of theresidual photoacid generator by heating. Further a minor amount of athermal acid generator capable of generating an acid upon heating may beadded to the resist composition.

The first resist pattern based on the polymer comprising recurring unitshaving 7-oxanorbornane rings and recurring units having acid labilegroups is converted into a film which is alkali soluble as a result ofdeprotection of acid labile groups and into a film which is insoluble ina solvent (i.e., solvent in a reversal film or second resistpattern-forming composition) as a result of crosslinking of7-oxanorbornane ring. Therefore, even when a solution of reversal orsecond resist film-forming material in an organic solvent is coated onthe first resist pattern, no intermixing occurs between the first resistpattern and the reversal film-forming second resist composition.

During subsequent treatment with an alkaline developer for patterningthe second resist film, a surface layer of the reversal or second resistfilm is dissolved down to the level of the first resist pattern, afterwhich dissolution of the first resist pattern is commenced, wherebyimage reversal is accomplished. With respect to the dissolutionmechanism that the second resist film (subject to reversal transfer)overlying the first resist pattern is dissolved down to the level of thereversed first resist pattern, the second resist film subject toreversal transfer may be previously given a rate of alkalinedissolution. Alternatively, the acid present in the first resist patternreacts with acid labile groups in the second resist film overlying thefirst resist pattern during the prebaking and post-exposure baking inthe second resist patterning process whereby the acid labile groups areeliminated so that the second resist film is converted to be alkalisoluble, allowing the alkaline developer to reach the reversed firstresist pattern whereby the first resist pattern can be dissolved away inthe alkaline developer and removed.

If a polymer comprising oxirane or oxetane-bearing recurring units isused as the resist base resin, it fails to function as the desired firstpositive resist material in the inventive process, because the oxiraneor oxetane ring has so high a rate of acid-catalyzed cleavage reactionthat crosslinking takes place at the resist processing temperature, forexample, a post-exposure baking (PEB) temperature of about 90 to 130°C., whereby the polymer becomes alkali insoluble. In contrast, theinventive polymer undergoes no crosslinking at the heating temperaturerange of PEB because the 1,4-epoxy bond of 7-oxanorbornane ring is lowreactive in the acid-catalyzed cleavage reaction as compared with theoxirane or oxetane ring. The recurring units having 7-oxanorbornane ringare stable relative to acid during the process until development, andserve as hydrophilic groups to exert the function of improving adhesionand alkali solubility. However, under the action of acid remaining inthe pattern after development or acid generated upon heating and heatingat or above 160° C., the 1,4-epoxy bond of 7-oxanorbornane ring iscleaved so that crosslinking reaction takes place whereby the polymerbecomes insoluble in the solvent and at the same time, the acid and heatcause deprotection of acid labile groups whereby alkali solubility isincreased.

The base resin in the first positive resist composition used in thepattern forming process is advantageously a polymer comprisingcrosslinkable recurring units represented by the general formula (a) andrecurring units having an acid labile group represented by the followinggeneral formula (b).

Herein R⁶ is hydrogen or methyl, R⁷ is an acid labile group, and b is anumber in the range: 0<b≦0.8.

The monomers from which recurring units of formula (b) are derived aremonomers Mb of the following general formula wherein R⁶ and R⁷ are asdefined above.

The acid labile group represented by R⁷ in formula (b) may be selectedfrom a variety of such groups, specifically groups of the followingformulae (AL-10) and (AL-11), tertiary alkyl groups of the followingformula (AL-12), and oxoalkyl groups of 4 to 20 carbon atoms, but notlimited thereto.

In formulae (AL-10) and (AL-11), R⁵¹ and R⁵⁴ each are a monovalenthydrocarbon group, typically a straight, branched or cyclic alkyl groupof 1 to 40 carbon atoms, more specifically 1 to 20 carbon atoms, whichmay contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine.The subscript “a5” is an integer of 0 to 10, and especially 1 to 5. R⁵²and R⁵³ each are hydrogen or a monovalent hydrocarbon group, typically astraight, branched or cyclic C₁-C₂₀ alkyl group, which may contain aheteroatom such as oxygen, sulfur, nitrogen or fluorine. Alternatively,a pair of R⁵² and R⁵³, R⁵² and R⁵⁴, or R⁵³ and R⁵⁴, taken together, mayform a ring, specifically aliphatic ring, with the carbon atom or thecarbon and oxygen atoms to which they are attached, the ring having 3 to20 carbon atoms, especially 4 to 16 carbon atoms.

In formula (AL-12), R⁵⁵, R⁵⁶ and R⁵⁷ each are a monovalent hydrocarbongroup, typically a straight, branched or cyclic C₁-C₂₀ alkyl group,which may contain a heteroatom such as oxygen, sulfur, nitrogen orfluorine. Alternatively, a pair of R⁵⁵ and R⁵⁶, R⁵⁵ and R⁵⁷, or R⁵⁶ andR⁵⁷, taken together, may form a ring, specifically aliphatic ring, withthe carbon atom to which they are attached, the ring having 3 to 20carbon atoms, especially 4 to 16 carbon atoms.

Illustrative examples of the groups of formula (AL-10) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl and2-tetrahydrofuranyloxycarbonylmethyl as well as substituent groups ofthe following formulae (AL-10)-1 to (AL-10)-10.

In formulae (AL-10)-1 to (AL-10)-10, R⁵ is independently a straight,branched or cyclic C₁-C₈ alkyl group, C₆-C₂₀ aryl group or C₇-C₂₀aralkyl group; R⁵⁹ is hydrogen or a straight, branched or cyclic C₁-C₂₀alkyl group; R⁶⁰ is a C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group; and“a5” is an integer of 0 to 10.

Illustrative examples of the acetal group of formula (AL-11) includethose of the following formulae (AL-11)-1 to (AL-11)-34.

Other examples of acid labile groups include those of the followingformula (AL-11a) or (AL-11b) while the polymer may be crosslinked withinthe molecule or between molecules with these acid labile groups.

Herein R⁶¹ and R⁶² each are hydrogen or a straight, branched or cyclicC₁-C₈ alkyl group, or R⁶¹ and R⁶², taken together, may form a ring withthe carbon atom to which they are attached, and R⁶¹ and R⁶² are straightor branched C₁-C₈ alkylene groups when they form a ring. R⁶³ is astraight, branched or cyclic C₁-C₁₀ alkylene group. Each of b5 and d5 is0 or an integer of 1 to 10, preferably 0 or an integer of 1 to 5, and c5is an integer of 1 to 7. “A” is a (c5+1)-valent aliphatic or alicyclicsaturated hydrocarbon group, aromatic hydrocarbon group or heterocyclicgroup having 1 to 50 carbon atoms, which may be separated by aheteroatom such as oxygen, sulfur or nitrogen or in which some of thehydrogen atoms attached to carbon atoms may be substituted by hydroxyl,carboxyl, carbonyl groups or fluorine atoms. “B” is —CO—O—, —NHCO—O— or—NHCONH—.

Preferably, “A” is selected from divalent to tetravalent, straight,branched or cyclic C₁-C₂₀ alkylene, alkanetriyl and alkanetetraylgroups, and C₆-C₃₀ arylene groups, which may be separated by aheteroatom such as oxygen, sulfur or nitrogen or in which some of thehydrogen atoms attached to carbon atoms may be substituted by hydroxyl,carboxyl, acyl groups or halogen atoms. The subscript c5 is preferablyan integer of 1 to 3.

The crosslinking acetal groups of formulae (AL-11a) and (AL-11b) areexemplified by the following formulae through (AL-11)-42.

Illustrative examples of the tertiary alkyl of formula (AL-12) includetert-butyl, triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl,1-ethylcyclopentyl, and tert-amyl groups as well as those of (AL-12)-1to (AL-12)-16.

Herein R⁶⁴ is independently a straight, branched or cyclic C₁-C₈ alkylgroup, C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group; R⁶⁵ and R⁶⁷ each arehydrogen or a straight, branched or cyclic C₁-C₂₀ alkyl group; and R⁶⁶is a C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group.

With R⁶⁸ representative of a di- or more valent alkylene or arylenegroup included as shown in formulae (AL-12)-17 and (AL-12)-18, thepolymer may be crosslinked within the molecule or between molecules. Informulae (AL-12)-17 and (AL-12)-18, R⁶⁴ is as defined above; R⁶⁸ is astraight, branched or cyclic C₁-C₂₀ alkylene group or arylene group,which may contain a heteroatom such as oxygen, sulfur or nitrogen; andb6 is an integer of 1 to 3.

The groups represented by R⁶⁴, R⁶⁵, R⁶⁶ and R⁶⁷ may contain a heteroatomsuch as oxygen, nitrogen or sulfur. Such groups are exemplified by thoseof the following formulae (AL-13)-1 to (AL-13)-7.

Of the acid labile groups of formula (AL-12), recurring units having anexo-form structure represented by the formula (AL-12)-19 are preferred.

Herein, R⁶⁹ is a straight, branched or cyclic C₁-C₈ alkyl group or asubstituted or unsubstituted C₆-C₂₀ aryl group; R⁷⁰ to R⁷⁵, R⁷⁸ and R⁷⁹are each independently hydrogen or a monovalent hydrocarbon group,typically alkyl, of 1 to 15 carbon atoms which may contain a heteroatom;and R⁷⁶ and R⁷⁷ are hydrogen. Alternatively, a pair of R⁷⁰ and R⁷¹, R⁷²and R⁷⁴, R⁷² and R⁷⁵, R⁷³ and R⁷⁵, R⁷³ and R⁷⁹, R⁷⁴ and R⁷⁸, R⁷⁶ andR⁷⁷, or R⁷⁸, taken together, may form a ring, specifically aliphaticring, with the carbon atom(s) to which they are attached, and in thiscase, each R is a divalent hydrocarbon group, typically alkylene, of 1to 15 carbon atoms which may contain a heteroatom. Also, a pair of R⁷⁰and R⁷⁹, R⁷⁶ and R⁷⁹, or R⁷² and R⁷⁴ which are attached to vicinalcarbon atoms may bond together directly to form a double bond. Theformula also represents an enantiomer.

The ester form monomers from which recurring units having an exo-formstructure represented by the formula (AL-12)-19:

are derived are described in U.S. Pat. No. 6,448,420 (JP-A 2000-327633).It is noted that R and R are each independently hydrogen, methyl,—COOCH₃, —CH₂COOCH₃ or the like. Illustrative non-limiting examples ofsuitable monomers are given below.

Also included in the acid labile groups of formula (AL-12) are acidlabile groups having furandiyl, tetrahydrofurandiyl or oxanorbornanediylas represented by the following formula (AL-12)-20.

Herein, R⁸⁰ and R⁸¹ are each independently a monovalent hydrocarbongroup, typically a straight, branched or cyclic C₁-C₁₀ alkyl. R⁸⁰ andR⁸¹, taken together, may form an aliphatic hydrocarbon ring of 3 to 20carbon atoms with the carbon atom to which they are attached. R⁸² is adivalent group selected from furandiyl, tetrahydrofurandiyl andoxanorbornanediyl. R⁸³ is hydrogen or a monovalent hydrocarbon group,typically a straight, branched or cyclic C₁-C₁₀ alkyl, which may containa heteroatom.

Examples of the monomers from which the recurring units substituted withacid labile groups having furandiyl, tetrahydrofurandiyl andoxanorbornanediyl as represented by the formula:

(wherein R⁸⁰ to R⁸³, and R¹¹² are as defined above) are derived areshown below. Note that Me is methyl and Ac is acetyl.

While the polymer used herein preferably includes recurring units offormula (a) and recurring units of formula (b), it may havecopolymerized therein recurring units (d) derived from monomers havingadhesive groups such as hydroxy, cyano, carbonyl, ester, ether groups,lactone rings, carbonyl groups or carboxylic anhydride groups. Examplesof monomers from which recurring units (d) are derived are given below.

Of the recurring units (d), those having an α-trifluoromethyl alcoholgroup or carboxyl group are preferably incorporated in copolymersbecause they improve the alkali dissolution rate of the developedpattern after heating. Examples of recurring units having a carboxylgroup are given below.

In the polymer of the invention, the recurring units (a), (b) and (d)are present in proportions a, b, and d, respectively, which satisfy therange: 0<a<1.0, 0<b≦0.8, 0.1≦a+b≦1.0, 0≦d<1.0, and preferably the range:0.1≦a≦0.9, 0.1≦b≦0.7, 0.2≦a+b≦1.0, and 0≦d≦0.9, provided that a+b+d=1.

It is noted that the meaning of a+b=1 is that in a polymer comprisingrecurring units (a) and (b), the sum of recurring units (a) and (b) is100 mol % based on the total amount of entire recurring units. Themeaning of a+b<1 is that the sum of recurring units (a) and (b) is lessthan 100 mol % based on the total amount of entire recurring units,indicating the inclusion of other recurring units, for example, units(d).

The polymer serving as the base resin in the resist material used in thepattern forming process of the invention should preferably have a weightaverage molecular weight (Mw) in the range of 1,000 to 500,000, and morepreferably 2,000 to 30,000, as measured by gel permeation chromatography(GPC) using polystyrene standards. With too low a Mw, the efficiency ofthermal crosslinking in the resist material after development may becomelow. With too high a Mw, the polymer may lose alkali solubility and giverise to a footing phenomenon after pattern formation.

If a polymer has a wide molecular weight distribution or dispersity(Mw/Mn), which indicates the presence of lower and higher molecularweight polymer fractions, there is a possibility that foreign matter isleft on the pattern or the pattern profile is degraded. The influencesof molecular weight and dispersity become stronger as the pattern rulebecomes finer. Therefore, the multi-component copolymer shouldpreferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0, especially1.0 to 1.5, in order to provide a resist composition suitable formicropatterning to a small feature size.

It is understood that a blend of two or more polymers which differ incompositional ratio, molecular weight or dispersity is acceptable.

The polymer as used herein may be synthesized by any desired method, forexample, by dissolving unsaturated bond-containing monomerscorresponding to the respective units (a), (b) and (d) in an organicsolvent, adding a radical initiator thereto, and effecting heatpolymerization. Examples of the organic solvent which can be used forpolymerization include toluene, benzene, tetrahydrofuran, diethyl etherand dioxane. Examples of the polymerization initiator used hereininclude 2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is 2 to 100 hours, preferably 5 to 20hours. The acid labile group that has been incorporated in the monomersmay be kept as such, or the acid labile group may be once removed withan acid catalyst and thereafter protected or partially protected.

As described previously, the pattern forming process of the inventioncomprises the steps of coating the positive resist composition describedabove onto a substrate, prebaking the resist composition to form aresist film, exposing a selected area of the resist film to high-energyradiation, post-exposure baking, and developing the resist film with analkaline developer to dissolve the exposed area thereof to form a resistpattern such as a line pattern. The subsequent step is to treat theresist pattern (area unexposed to high-energy radiation) so as toutilize the acid remaining in the resist pattern or to generate acid,thereby eliminating acid labile groups on the polymer (i.e.,deprotection) and inducing crosslinking in the polymer. In thisdeprotected and crosslinked state, the polymer has a dissolution rate inexcess of 2 nm/sec, preferably of 3 to 5,000 nm/sec, and more preferably4 to 4,000 nm/sec in an alkaline developer. It is preferred in attainingthe objects of the invention that the dissolution rate of the polymer ishigher than the dissolution rate of the second resist material to form areversal film in the same alkaline developer by a factor of 2 to250,000, and especially 5 to 10,000.

In order that the polymer have a desired dissolution rate in thedeprotected and crosslinked state, the polymer formulation is preferablydesigned such that the acid labile group-bearing recurring units offormula (b) account for 10 mol % to 90 mol %, and more preferably 12 mol% to 80 mol % of the entire recurring units.

First Resist Composition

The resist composition, specifically chemically amplified positiveresist composition, used in the pattern forming process of the inventionmay further comprise an organic solvent, a compound capable ofgenerating an acid in response to high-energy radiation (known as “acidgenerator”), and optionally, a dissolution inhibitor, a basic compound,a surfactant, and other components.

Solvent

The organic solvent used herein may be any organic solvent in which thebase resin, acid generator, and other components are soluble.Illustrative, non-limiting, examples of the organic solvent includeketones such as cyclohexanone and methyl-2-n-amylketone; alcohols suchas 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol,and 1-ethoxy-2-propanol; ethers such as propylene glycol monomethylether, ethylene glycol monomethyl ether, propylene glycol monoethylether, ethylene glycol monoethyl ether, propylene glycol dimethyl ether,and diethylene glycol dimethyl ether; esters such as propylene glycolmonomethyl ether acetate, propylene glycol monoethyl ether acetate,ethyl lactate, ethyl pyruvate, butyl acetate, methyl3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate,tert-butyl propionate, and propylene glycol mono-tert-butyl etheracetate; and lactones such as γ-butyrolactone. These solvents may beused alone or in combinations of two or more thereof. Of the aboveorganic solvents, diethylene glycol dimethyl ether, 1-ethoxy-2-propanoland propylene glycol monomethyl ether acetate, and mixtures thereof arepreferred because the acid generator is most soluble therein.

The organic solvent is preferably used in an amount of about 200 to3,000 parts by weight, more preferably about 400 to 2,000 parts byweight per 100 parts by weight of the base resin.

Acid Generator

The acid generators used herein include the following:

(i) onium salts of the formula (P1a-1), (P1a-2), (P1a-3) or (P1b),

(ii) diazomethane derivatives of the formula (P2),

(iii) glyoxime derivatives of the formula (P3),

(iv) bissulfone derivatives of the formula (P4),

(v) sulfonic acid esters of N-hydroxyimide compounds of the formula(P5),

(vi) β-ketosulfonic acid derivatives,

(vii) disulfone derivatives,

(viii) nitrobenzylsulfonate derivatives, and

-   (ix) sulfonate derivatives.

These acid generators are described in detail.

(i) Onium Salts of Formula (P1a-1), (P1a-2) and (P1a-3):

Herein, R^(101a), R^(101b), and R^(101c) independently representstraight, branched or cyclic alkyl, alkenyl, oxoalkyl or oxoalkenylgroups of 1 to 12 carbon atoms, aryl groups of 6 to 20 carbon atoms, oraralkyl or aryloxoalkyl groups of 7 to 12 carbon atoms, wherein some orall of the hydrogen atoms may be replaced by alkoxy groups. Also,R^(101b) and R^(101c), taken together, may form a ring with the sulfuror iodine atom to which they are attached. R^(101b) and R^(101c) eachare alkylene groups of 1 to 6 carbon atoms when they form a ring. K⁻ isa sulfonate in which at least one alpha-position is fluorinated, or aperfluoroalkylimidate or perfluoroalkylmethidate. R^(101d), R^(101e),R^(101f), and R^(101g) stand for hydrogen atoms, straight, branched orcyclic alkyl, alkenyl, oxoalkyl or oxoalkenyl groups of 1 to 12 carbonatoms, aryl groups of 6 to 20 carbon atoms, or aralkyl or aryloxoalkylgroups of 7 to 12 carbon atoms, wherein some or all of the hydrogenatoms may be replaced by alkoxy groups. A pair of R^(101d) and R^(101e)or a combination of R^(101d), R^(101e) and R^(101f) may form a ring withthe nitrogen atom to which they are attached, and each of R^(101d) andR^(101e) or each of R^(101d), R^(101e) and R^(101f) is an alkylene groupof 3 to 10 carbon atoms or a hetero-aromatic ring having the nitrogenatom (in the formula) incorporated therein, when they form a ring.

Of the onium salts having formulae (P1a-1), (P1a-2) and (P1a-3), thoseof formula (P1a-1) function as a photoacid generator, those of formula(P1a-2) function as a thermal acid generator, and those of formula(P1a-3) have both the functions of a photoacid generator and a thermalacid generator. In a system having (P1a-1) combined with (P1a-2),generator (P1-a) generates an acid upon exposure, with which patternformation is performed, and generator (P1a-2) generates an acid whenheated at high temperature after development, with which crosslinking isefficiently performed.

Examples of K⁻ include perfluoroalkanesulfonates such as triflate andnonaflate; imidates such as bis(trifluoromethylsulfonyl)imide,bis(perfluoroethylsulfonyl)imide, and bis(perfluorobutylsulfonyl)imide;methidates such as tris(trifluoromethylsulfonyl)methide andtris(perfluoroethylsulfonyl)methide; sulfonates having fluorinesubstituted at α-position as represented by of the general formula (K-1)and sulfonates having fluorine substituted at α-position as representedby of the general formula (K-2).

In formula (K-1), R^(102a) is a hydrogen atom, or a straight, branchedor cyclic C₁-C₂₀ alkyl or acyl group, C₂-C₂₀ alkenyl group, or C₆-C₂₀aryl or aryloxy group, which may have an ether group, ester group,carbonyl group or lactone ring, or in which some or all hydrogen atomsmay be substituted by fluorine atoms. In formula (K-2), R^(102b) is ahydrogen atom, or a straight, branched or cyclic C₁-C₂₀ alkyl group,C₂-C₂₀ alkenyl group, or C₆-C₂₀ aryl group.

R^(101a), R^(101b), and R^(101c) may be the same or different and areillustrated below. Exemplary alkyl groups include methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl,cyclopentyl, cyclohexyl, cycloheptyl, cyclopropylmethyl,4-methylcyclohexyl, cyclohexylmethyl, norbornyl, and adamantyl.Exemplary alkenyl groups include vinyl, allyl, propenyl, butenyl,hexenyl, and cyclohexenyl. Exemplary oxoalkyl groups include2-oxocyclopentyl and 2-oxocyclohexyl as well as 2-oxopropyl,2-cyclopentyl-2-oxoethyl, 2-cyclohexyl-2-oxoethyl, and2-(4-methylcyclohexyl)-2-oxoethyl. Exemplary oxoalkenyl groups include2-oxo-4-cyclohexenyl and 2-oxo-4-propenyl. Exemplary aryl groups includephenyl and naphthyl; alkoxyphenyl groups such as p-methoxyphenyl,m-methoxyphenyl, o-methoxyphenyl, ethoxyphenyl, p-tert-butoxyphenyl, andm-tert-butoxyphenyl; alkylphenyl groups such as 2-methylphenyl,3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl,4-butylphenyl, and dimethylphenyl; alkylnaphthyl groups such asmethylnaphthyl and ethylnaphthyl; alkoxynaphthyl groups such asmethoxynaphthyl and ethoxynaphthyl; dialkylnaphthyl groups such asdimethylnaphthyl and diethylnaphthyl; and dialkoxynaphthyl groups suchas dimethoxynaphthyl and diethoxynaphthyl. Exemplary aralkyl groupsinclude benzyl, phenylethyl, and phenethyl. Exemplary aryloxoalkylgroups are 2-aryl-2-oxoethyl groups such as 2-phenyl-2-oxoethyl,2-(1-naphthyl)-2-oxoethyl, and 2-(2-naphthyl)-2-oxoethyl.

Examples of the non-nucleophilic counter ion represented by K⁻ includehalide ions such as chloride and bromide ions; fluoroalkylsulfonate ionssuch as triflate, 1,1,1-trifluoroethanesulfonate, andnonafluorobutanesulfonate; arylsulfonate ions such as tosylate,benzenesulfonate, 4-fluorobenzenesulfonate,1,2,3,4,5-pentafluorobenzenesulfonate; and alkylsulfonate ions such asmesylate and butanesulfonate.

Herein, R^(102a) and R^(102b) independently represent straight, branchedor cyclic alkyl groups of 1 to 8 carbon atoms. R¹⁰³ represents astraight, branched or cyclic alkylene group of 1 to 10 carbon atoms.R^(104a) and R^(104b) independently represent 2-oxoalkyl groups of 3 to7 carbon atoms. K⁻ is a non-nucleophilic counter ion.

Illustrative of the groups represented by R^(102a) and R^(102b) aremethyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl,pentyl, hexyl, heptyl, octyl, cyclopentyl, cyclohexyl,cyclopropylmethyl, 4-methylcyclohexyl, and cyclohexylmethyl.Illustrative of the groups represented by R¹⁰³ are methylene, ethylene,propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene,1,4-cyclohexylene, 1,2-cyclohexylene, 1,3-cyclopentylene,1,4-cyclooctylene, and 1,4-cyclohexanedimethylene. Illustrative of thegroups represented by R^(104a) and R^(104b) are 2-oxopropyl,2-oxocyclopentyl, 2-oxocyclohexyl, and 2-oxocycloheptyl. Illustrativeexamples of the counter ion represented by K⁻ are the same asexemplified for formulae (P1a-1) and (P1a-2).

(ii) Diazomethane Derivatives of Formula (P2)

Herein, R¹⁰⁵ and R¹⁰⁶ independently represent straight, branched orcyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms, arylor halogenated aryl groups of 6 to 20 carbon atoms, or aralkyl groups of7 to 12 carbon atoms.

Of the groups represented by R¹⁰⁵ and R¹⁰⁶, exemplary alkyl groupsinclude methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl,tert-butyl, pentyl, hexyl, heptyl, octyl, amyl, cyclopentyl, cyclohexyl,cycloheptyl, norbornyl, and adamantyl. Exemplary halogenated alkylgroups include trifluoromethyl, 1,1,1-trifluoroethyl,1,1,1-trichloroethyl, and nonafluorobutyl. Exemplary aryl groups includephenyl; alkoxyphenyl groups such as p-methoxyphenyl, m-methoxyphenyl,o-methoxyphenyl, ethoxyphenyl, p-tert-butoxyphenyl, andm-tert-butoxyphenyl; and alkylphenyl groups such as 2-methylphenyl,3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl,4-butylphenyl, and dimethylphenyl. Exemplary halogenated aryl groupsinclude fluorophenyl, chlorophenyl, and 1,2,3,4,5-pentafluorophenyl.Exemplary aralkyl groups include benzyl and phenethyl.

(iii) Glyoxime Derivatives of Formula (P3)

Herein, R¹⁰⁷ R¹⁰⁸ and R¹⁰⁹ independently represent straight, branched orcyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms, arylor halogenated aryl groups of 6 to 20 carbon atoms, or aralkyl groups of7 to 12 carbon atoms. Also, R¹⁰⁸ and R¹⁰⁹, taken together, may form acyclic structure. R¹⁰⁸ and R¹⁰⁹ each are a straight or branched alkylenegroup of 1 to 6 carbon atoms when they form a cyclic structure. R¹⁰⁵ isas defined in formula (P2).

Illustrative examples of the alkyl, halogenated alkyl, aryl, halogenatedaryl, and aralkyl groups represented by R¹⁰⁷, R¹⁰⁸, and R¹⁰⁹ are thesame as exemplified for R¹⁰⁵ and R¹⁰⁶. Examples of the alkylene groupsrepresented by R¹⁰⁸ and R¹⁰⁹ include methylene, ethylene, propylene,butylene, and hexylene.

(iv) Bissulfone Derivatives of Formula (P4)

Herein, R^(101a) and R^(101b) are as defined above.

(v) Sulfonic Acid Esters of N-Hydroxyimide Compounds of Formula (P5)

Herein, R¹¹⁰ is an arylene group of 6 to 10 carbon atoms, alkylene groupof 1 to 6 carbon atoms, or alkenylene group of 2 to 6 carbon atomswherein some or all of the hydrogen atoms may be replaced by straight orbranched alkyl or alkoxy groups of 1 to 4 carbon atoms, nitro, acetyl,or phenyl groups. R¹¹¹ is a straight, branched or cyclic alkyl group of1 to 8 carbon atoms, alkenyl, alkoxyalkyl, phenyl or naphthyl groupwherein some or all of the hydrogen atoms may be replaced by alkyl oralkoxy groups of 1 to 4 carbon atoms, phenyl groups (which may havesubstituted thereon an alkyl or alkoxy of 1 to 4 carbon atoms, nitro, oracetyl group), hetero-aromatic groups of 3 to 5 carbon atoms, orchlorine or fluorine atoms.

Of the groups represented by R¹¹⁰, exemplary arylene groups include1,2-phenylene and 1,8-naphthylene; exemplary alkylene groups includemethylene, ethylene, trimethylene, tetramethylene, phenylethylene, andnorbornane-2,3-diyl; and exemplary alkenylene groups include1,2-vinylene, 1-phenyl-1,2-vinylene, and 5-norbornene-2,3-diyl. Of thegroups represented by R¹¹¹, exemplary alkyl groups are as exemplifiedfor R^(101a) to R^(101c); exemplary alkenyl groups include vinyl,1-propenyl, allyl, 1-butenyl, 3-butenyl, isoprenyl, 1-pentenyl,3-pentenyl, 4-pentenyl, dimethylallyl, 1-hexenyl, 3-hexenyl, 5-hexenyl,1-heptenyl, 3-heptenyl, 6-heptenyl, and 7-octenyl; and exemplaryalkoxyalkyl groups include methoxymethyl, ethoxymethyl, propoxymethyl,butoxymethyl, pentyloxymethyl, hexyloxymethyl, heptyloxymethyl,methoxyethyl, ethoxyethyl, propoxyethyl, butoxyethyl, pentyloxyethyl,hexyloxyethyl, methoxypropyl, ethoxypropyl, propoxypropyl, butoxypropyl,methoxybutyl, ethoxybutyl, propoxybutyl, methoxypentyl, ethoxypentyl,methoxyhexyl, and methoxyheptyl.

Of the substituents on these groups, the alkyl groups of 1 to 4 carbonatoms include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl andtert-butyl; and the alkoxy groups of 1 to 4 carbon atoms includemethoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy, andtert-butoxy. The phenyl groups which may have substituted thereon analkyl or alkoxy of 1 to 4 carbon atoms, nitro, or acetyl group includephenyl, tolyl, p-tert-butoxyphenyl, p-acetylphenyl and p-nitrophenyl.The hetero-aromatic groups of 3 to 5 carbon atoms include pyridyl andfuryl.

Illustrative examples of the acid generator include:

onium salts such as diphenyliodonium trifluoromethanesulfonate,(p-tert-butoxyphenyl)phenyliodonium trifluoromethanesulfonate,diphenyliodonium p-toluenesulfonate, (p-tert-butoxyphenyl)phenyliodoniump-toluenesulfonate, triphenylsulfonium trifluoromethanesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,bis(p-tert-butoxyphenyl)phenylsulfonium trifluoromethanesulfonate,tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate,triphenylsulfonium p-toluenesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate,bis(p-tert-butoxyphenyl)phenylsulfonium p-toluenesulfonate,tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate,triphenylsulfonium nonafluorobutanesulfonate, triphenylsulfoniumbutanesulfonate, trimethylsulfonium trifluoromethanesulfonate,trimethylsulfonium p-toluenesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium p-toluenesulfonate,dimethylphenylsulfonium trifluoromethanesulfonate,dimethylphenylsulfonium p-toluenesulfonate, dicyclohexylphenylsulfoniumtrifluoromethanesulfonate, dicyclohexylphenylsulfoniump-toluenesulfonate, trinaphthylsulfonium trifluoromethanesulfonate,(2-norbornyl)methyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,ethylenebis[methyl(2-oxocyclopentyl)sulfoniumtrifluoromethanesulfonate], and1,2′-naphthylcarbonylmethyltetrahydrothiophenium triflate;

diazomethane derivatives such as bis(benzenesulfonyl)diazomethane,bis(p-toluenesulfonyl)diazomethane, bis(xylenesulfonyl)diazomethane,bis(cyclohexylsulfonyl)diazomethane,bis(cyclopentylsulfonyl)diazomethane, bis(n-butylsulfonyl)diazomethane,bis(isobutylsulfonyl)diazomethane, bis(sec-butylsulfonyl)diazomethane,bis(n-propylsulfonyl)diazomethane, bis(isopropylsulfonyl)diazomethane,bis(tert-butylsulfonyl)diazomethane, bis(n-amylsulfonyl)diazomethane,bis(isoamylsulfonyl)diazomethane, bis(sec-amylsulfonyl)diazomethane,bis(tert-amylsulfonyl)diazomethane,1-cyclohexylsulfonyl-1-(tert-butylsulfonyl)diazomethane,1-cyclohexylsulfonyl-1-(tert-amylsulfonyl)diazomethane, and1-tert-amylsulfonyl-1-(tert-butylsulfonyl)diazomethane;

glyoxime derivatives such asbis-O-(p-toluenesulfonyl)-α-dimethylglyoxime,bis-O-(p-toluenesulfonyl)-α-diphenylglyoxime,bis-O-(p-toluenesulfonyl)-α-dicyclohexylglyoxime,bis-O-(p-toluenesulfonyl)-2,3-pentanedioneglyoxime,bis-O-(p-toluenesulfonyl)-2-methyl-3,4-pentanedioneglyoxime,bis-O-(n-butanesulfonyl)-α-dimethylglyoxime,bis-O-(n-butanesulfonyl)-α-diphenylglyoxime,bis-O-(n-butanesulfonyl)-α-dicyclohexylglyoxime,bis-O-(n-butanesulfonyl)-2,3-pentanedioneglyoxime,bis-O-(n-butanesulfonyl)-2-methyl-3,4-pentanedioneglyoxime,bis-O-(methanesulfonyl)-α-dimethylglyoxime,bis-O-(trifluoromethanesulfonyl)-α-dimethylglyoxime,bis-O-(1,1,1-trifluoroethanesulfonyl)-α-dimethylglyoxime,bis-O-(tert-butanesulfonyl)-α-dimethylglyoxime,bis-O-(perfluorooctanesulfonyl)-α-dimethylglyoxime,bis-O-(cyclohexanesulfonyl)-α-dimethylglyoxime,bis-O-(benzenesulfonyl)-α-dimethylglyoxime,bis-O-(p-fluorobenzenesulfonyl)-α-dimethylglyoxime,bis-O-(p-tert-butylbenzenesulfonyl)-α-dimethylglyoxime,bis-O-(xylenesulfonyl)-α-dimethylglyoxime, andbis-O-(camphorsulfonyl)-α-dimethylglyoxime;

bissulfone derivatives such as bisnaphthylsulfonylmethane,bistrifluoromethylsulfonylmethane, bismethylsulfonylmethane,bisethylsulfonylmethane, bispropylsulfonylmethane,bisisopropylsulfonylmethane, bis-p-toluenesulfonylmethane, andbisbenzenesulfonylmethane;

β-ketosulfone derivatives such as2-cyclohexylcarbonyl-2-(p-toluenesulfonyl)propane and2-isopropylcarbonyl-2-(p-toluenesulfonyl)propane;

disulfone derivatives such as diphenyl disulfone deratives anddicyclohexyl disulfone derivatives;

nitrobenzyl sulfonate derivatives such as 2,6-dinitrobenzylp-toluenesulfonate and 2,4-dinitrobenzyl p-toluenesulfonate;

sulfonic acid ester derivatives such as1,2,3-tris(methanesulfonyloxy)benzene,1,2,3-tris(trifluoromethanesulfonyloxy)benzene, and1,2,3-tris(p-toluenesulfonyloxy)benzene; and

sulfonic acid esters of N-hydroxyimides such as N-hydroxysuccinimidemethanesulfonate, N-hydroxysuccinimide trifluoromethanesulfonate,N-hydroxysuccinimide ethanesulfonate, N-hydroxysuccinimide1-propanesulfonate, N-hydroxysuccinimide 2-propanesulfonate,N-hydroxysuccinimide 1-pentanesulfonate, N-hydroxysuccinimide1-octanesulfonate, N-hydroxysuccinimide p-toluenesulfonate,N-hydroxysuccinimide p-methoxybenzenesulfonate, N-hydroxysuccinimide2-chloroethanesulfonate, N-hydroxysuccinimide benzenesulfonate,N-hydroxysuccinimide 2,4,6-trimethylbenzenesulfonate,N-hydroxysuccinimide 1-naphthalenesulfonate, N-hydroxysuccinimide2-naphthalenesulfonate, N-hydroxy-2-phenylsuccinimide methanesulfonate,N-hydroxymaleimide methanesulfonate, N-hydroxymaleimide ethanesulfonate,N-hydroxy-2-phenylmaleimide methanesulfonate, N-hydroxyglutarimidemethanesulfonate, N-hydroxyglutarimide benzenesulfonate,N-hydroxyphthalimide methanesulfonate, N-hydroxyphthalimidebenzenesulfonate, N-hydroxyphthalimide trifluoromethanesulfonate,N-hydroxyphthalimide p-toluenesulfonate, N-hydroxynaphthalimidemethanesulfonate, N-hydroxynaphthalimide benzenesulfonate,N-hydroxy-5-norbornene-2,3-dicarboxyimide methanesulfonate,N-hydroxy-5-norbornene-2,3-dicarboxyimide trifluoromethanesulfonate, andN-hydroxy-5-norbornene-2,3-dicarboxyimide p-toluenesulfonate.

Preferred among these acid generators are onium salts such astriphenylsulfonium trifluoromethanesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate,triphenylsulfonium p-toluenesulfonate,(p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate,tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate,trinaphthylsulfonium trifluoromethanesulfonate,cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate,(2-norbornyl)methyl(2-oxocylohexyl)sulfonium trifluoromethanesulfonate,and 1,2′-naphthylcarbonylmethyltetrahydrothiophenium triflate;

diazomethane derivatives such as bis(benzenesulfonyl)diazomethane,bis(p-toluenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane,bis(n-butylsulfonyl)diazomethane, bis(isobutylsulfonyl)diazomethane,bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)diazomethane,bis(isopropylsulfonyl)diazomethane, andbis(tert-butylsulfonyl)diazomethane;

glyoxime derivatives such asbis-O-(p-toluenesulfonyl)-α-dimethylglyoxime andbis-O-(n-butanesulfonyl)-α-dimethylglyoxime;

bissulfone derivatives such as bisnaphthylsulfonylmethane; and

sulfonic acid esters of N-hydroxyimide compounds such asN-hydroxysuccinimide methanesulfonate, N-hydroxysuccinimidetrifluoromethanesulfonate, N-hydroxysuccinimide 1-propanesulfonate,N-hydroxysuccinimide 2-propanesulfonate, N-hydroxysuccinimide1-pentanesulfonate, N-hydroxysuccinimide p-toluenesulfonate,N-hydroxynaphthalimide methanesulfonate, and N-hydroxynaphthalimidebenzenesulfonate.

Also useful are acid generators of the oxime type described in WO2004/074242 A2.

These acid generators may be used singly or in combinations of two ormore thereof. Onium salts are effective for improving rectangularity,while diazomethane derivatives and glyoxime derivatives are effectivefor reducing standing waves. The combination of an onium salt with adiazomethane or a glyoxime derivative allows for fine adjustment of theprofile.

The acid generator is preferably added in an amount of 0.1 to 50 parts,and especially 0.5 to 40 parts by weight, per 100 parts by weight of thebase resin. Less than 0.1 phr of the acid generator may generate a lessamount of acid upon exposure, sometimes leading to a poor sensitivityand resolution whereas more than 50 phr of the acid generator mayadversely affect the transmittance and resolution of resist. Forexample, where acid generators (P1a-1) and (P1a-2) are used incombination, they are mixed such that the mixture consists of 1 pbw of(P1a-1) and 0.001 to 1 pbw of (P1a-2) because generator (P1a-2)functions only as a thermal acid generator. Differently stated, theamount of thermal acid generator (P1a-2) added is preferably limited tosuch a level as to have no impact on the lithography of patterning thefirst resist film, no impact on the thermal properties of the firstresist film, and no impact on the second resist film, and specificallyto the range of 0.01 to 1 part by weight per 100 parts by weight of thebase resin.

Dissolution Inhibitor

To the positive resist composition, especially chemically amplifiedpositive resist composition, a dissolution inhibitor or regulator may beadded. The dissolution inhibitor is a compound having on the molecule atleast two phenolic hydroxyl groups, in which an average of from 0 to 100mol % of all the hydrogen atoms on the phenolic hydroxyl groups arereplaced with acid labile groups or a compound having on the molecule atleast one carboxyl group, in which an average of 50 to 100 mol % of allthe hydrogen atoms on the carboxyl groups are replaced with acid labilegroups, both the compounds having a weight average molecular weightwithin a range of 100 to 1,000, and preferably 150 to 800.

The degree of substitution of the hydrogen atoms on the phenolichydroxyl groups with acid labile groups is on average at least 0 mol %,and preferably at least 30 mol %, of all the phenolic hydroxyl groups.The upper limit is 100 mol %, and preferably 80 mol %. The degree ofsubstitution of the hydrogen atoms on the carboxyl groups with acidlabile groups is on average at least 50 mol %, and preferably at least70 mol %, of all the carboxyl groups, with the upper limit being 100 mol%.

Preferable examples of such compounds having two or more phenolichydroxyl groups or compounds having at least one carboxyl group includethose of formulas (D1) to (D14) below.

In these formulas, R²⁰¹ and R²⁰² are each hydrogen or a straight orbranched C₁-C₈ alkyl or alkenyl; R²⁰³ is hydrogen, a straight orbranched C₁-C₈ alkyl or alkenyl, or —(R²⁰⁷)_(h)—COOH; R is —(CH₂)_(i)—(where i=2 to 10), a C₆-C₁₀ arylene, carbonyl, sulfonyl, an oxygen atom,or a sulfur atom; R²⁰⁵ is a C₁-C₁₀ alkylene, a C₆-C₁₀ arylene, carbonyl,sulfonyl, an oxygen atom, or a sulfur atom; R²⁰⁶ is hydrogen, a straightor branched C₁-C₈ alkyl or alkenyl, or a hydroxyl-substituted phenyl ornaphthyl; R²⁰⁷ is a straight or branched C₁-C₁₀ alkylene; R²⁰⁸ ishydrogen or hydroxyl; the letter j is an integer from 0 to 5; u and hare each 0 or 1; s, t, s′, t′, s″, and t″ are each numbers which satisfys+t=8, s′+t′=5, and s″+t″=4, and are such that each phenyl structure hasat least one hydroxyl group; and α is a number such that the compoundsof formula (D8) or (D9) have a molecular weight of from 100 to 1,000.

The dissolution inhibitor may be formulated in an amount of 0 to 50parts, preferably 5 to 50 parts, and more preferably 10 to 30 parts byweight, per 100 parts by weight of the base resin, and may be usedsingly or as a mixture of two or more thereof. Outside the range, a lessamount of the dissolution inhibitor may fail to improve resolutionwhereas a larger amount may lead to slimming of the patterned film and adecline in resolution.

Basic Compound

The basic compound used herein is preferably a compound capable ofsuppressing the rate of diffusion when the acid generated by the acidgenerator diffuses within the resist film. The inclusion of this type ofbasic compound holds down the rate of acid diffusion within the resistfilm, resulting in better resolution. In addition, it suppresses changesin sensitivity following exposure, thus reducing substrate andenvironment dependence, as well as improving the exposure latitude andthe pattern profile.

Examples of suitable basic compounds include primary, secondary, andtertiary aliphatic amines, mixed amines, aromatic amines, heterocyclicamines, nitrogen-containing compounds having carboxyl group,nitrogen-containing compounds having sulfonyl group, nitrogen-containingcompounds having hydroxyl group, nitrogen-containing compounds havinghydroxyphenyl group, nitrogen-containing alcoholic compounds, amidederivatives, and imide derivatives.

Examples of suitable primary aliphatic amines include ammonia,methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine,iso-butylamine, sec-butylamine, tert-butylamine, pentylamine,tert-amylamine, cyclopentylamine, hexylamine, cyclohexylamine,heptylamine, octylamine, nonylamine, decylamine, dodecylamine,cetylamine, methylenediamine, ethylenediamine, andtetraethylenepentamine. Examples of suitable secondary aliphatic aminesinclude dimethylamine, diethylamine, di-n-propylamine,di-iso-propylamine, di-n-butylamine, di-iso-butylamine,di-sec-butylamine, dipentylamine, dicyclopentylamine, dihexylamine,dicyclohexylamine, diheptylamine, dioctylamine, dinonylamine,didecylamine, didodecylamine, dicetylamine,N,N-dimethylmethylenediamine, N,N-dimethylethylenediamine, andN,N-dimethyltetraethylenepentamine. Examples of suitable tertiaryaliphatic amines include trimethylamine, triethylamine,tri-n-propylamine, tri-iso-propylamine, tri-n-butylamine,tri-iso-butylamine, tri-sec-butylamine, tripentylamine,tricyclopentylamine, trihexylamine, tricyclohexylamine, triheptylamine,trioctylamine, trinonylamine, tridecylamine, tridodecylamine,tricetylamine, N,N,N′,N′-tetramethylmethylenediamine,N,N,N′,N′-tetramethylethylenediamine, andN,N,N′,N′-tetramethyltetraethylenepentamine.

Examples of suitable mixed amines include dimethylethylamine,methylethylpropylamine, benzylamine, phenethylamine, andbenzyldimethylamine.

Examples of suitable aromatic amines include aniline derivatives (e.g.,aniline, N-methylaniline, N-ethylaniline, N-propylaniline,N,N-dimethylaniline, 2-methylaniline, 3-methylaniline, 4-methylaniline,ethylaniline, propylaniline, trimethylaniline, 2-nitroaniline,3-nitroaniline, 4-nitroaniline, 2,4-dinitroaniline, 2,6-dinitroaniline,3,5-dinitroaniline, and N,N-dimethyltoluidine), diphenyl(p-tolyl)amine,methyldiphenylamine, triphenylamine, phenylenediamine, naphthylamine,and diaminonaphthalene. Examples of suitable heterocyclic amines includepyrrole derivatives (e.g., pyrrole, 2H-pyrrole, 1-methylpyrrole,2,4-dimethylpyrrole, 2,5-dimethylpyrrole, and N-methylpyrrole), oxazolederivatives (e.g., oxazole and isooxazole), thiazole derivatives (e.g.,thiazole and isothiazole), imidazole derivatives (e.g., imidazole,4-methylimidazole, and 4-methyl-2-phenylimidazole), pyrazolederivatives, furazan derivatives, pyrroline derivatives (e.g., pyrrolineand 2-methyl-1-pyrroline), pyrrolidine derivatives (e.g., pyrrolidine,N-methylpyrrolidine, pyrrolidinone, and N-methylpyrrolidone),imidazoline derivatives, imidazolidine derivatives, pyridine derivatives(e.g., pyridine, methylpyridine, ethylpyridine, propylpyridine,butylpyridine, 4-(1-butylpentyl)pyridine, dimethylpyridine,trimethylpyridine, triethylpyridine, phenylpyridine,3-methyl-2-phenylpyridine, 4-tert-butylpyridine, diphenylpyridine,benzylpyridine, methoxypyridine, butoxypyridine, dimethoxypyridine,1-methyl-2-pyridone, 4-pyrrolidinopyridine, 1-methyl-4-phenylpyridine,2-(1-ethylpropyl)pyridine, aminopyridine, and dimethylaminopyridine),pyridazine derivatives, pyrimidine derivatives, pyrazine derivatives,pyrazoline derivatives, pyrazolidine derivatives, piperidinederivatives, piperazine derivatives, morpholine derivatives, indolederivatives, isoindole derivatives, 1H-indazole derivatives, indolinederivatives, quinoline derivatives (e.g., quinoline and3-quinolinecarbonitrile), isoquinoline derivatives, cinnolinederivatives, quinazoline derivatives, quinoxaline derivatives,phthalazine derivatives, purine derivatives, pteridine derivatives,carbazole derivatives, phenanthridine derivatives, acridine derivatives,phenazine derivatives, 1,10-phenanthroline derivatives, adeninederivatives, adenosine derivatives, guanine derivatives, guanosinederivatives, uracil derivatives, and uridine derivatives.

Examples of suitable nitrogen-containing compounds having carboxyl groupinclude aminobenzoic acid, indolecarboxylic acid, and amino acidderivatives (e.g., nicotinic acid, alanine, alginine, aspartic acid,glutamic acid, glycine, histidine, isoleucine, glycylleucine, leucine,methionine, phenylalanine, threonine, lysine,3-aminopyrazine-2-carboxylic acid, and methoxyalanine). Examples ofsuitable nitrogen-containing compounds having sulfonyl group include3-pyridinesulfonic acid and pyridinium p-toluenesulfonate. Examples ofsuitable nitrogen-containing compounds having hydroxyl group,nitrogen-containing compounds having hydroxyphenyl group, andnitrogen-containing alcoholic compounds include 2-hydroxypyridine,aminocresol, 2,4-quinolinediol, 3-indolemethanol hydrate,monoethanolamine, diethanolamine, triethanolamine,N-ethyldiethanolamine, N,N-diethylethanolamine, triisopropanolamine,2,2′-iminodiethanol, 2-aminoethanol, 3-amino-1-propanol,4-amino-1-butanol, 4-(2-hydroxyethyl)morpholine,2-(2-hydroxyethyl)pyridine, 1-(2-hydroxyethyl)piperazine,1-[2-(2-hydroxyethoxy)ethyl]piperazine, piperidine ethanol,1-(2-hydroxyethyl)pyrrolidine, 1-(2-hydroxyethyl)-2-pyrrolidinone,3-piperidino-1,2-propanediol, 3-pyrrolidino-1,2-propanediol,8-hydroxyjulolidine, 3-quinuclidinol, 3-tropanol, 1-methyl-2-pyrrolidineethanol, 1-aziridine ethanol, N-(2-hydroxyethyl)phthalimide, andN-(2-hydroxyethyl)isonicotinamide.

Examples of suitable amide derivatives include formamide,N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide,N,N-dimethylacetamide, propionamide, and benzamide. Suitable imidederivatives include phthalimide, succinimide, and maleimide.

One or more basic compounds of the following general formula (B)-1 mayalso be added.N(X)_(n)(Y)_(3-n)  (B)-1

In the formula, n is equal to 1, 2 or 3; side chain Y is independentlyhydrogen or a straight, branched or cyclic alkyl group of 1 to 20 carbonatoms which may contain an ether or hydroxyl group; and side chain X isindependently selected from groups of the following general formulas(X)-1 to (X)-3, and two or three X's may bond together to form a ringwith the nitrogen atom to which they are attached.

In the formulas, R³⁰⁰, R³⁰² and R³⁰⁵ are independently straight orbranched alkylene groups of 1 to 4 carbon atoms; R³⁰¹ and R³⁰⁴ areindependently hydrogen, straight, branched or cyclic alkyl groups of 1to 20 carbon atoms, which may contain at least one hydroxyl, ether,ester group or lactone ring; R³⁰³ is a single bond or a straight orbranched alkylene group of 1 to 4 carbon atoms; and R³⁰⁶ is a straight,branched or cyclic alkyl group of 1 to 20 carbon atoms, which maycontain at least one hydroxyl, ether, ester group or lactone ring.

Illustrative examples of the compounds of formula (B)-1 includetris(2-methoxymethoxyethyl)amine, tris{2-(2-methoxyethoxy)ethyl}amine,tris{2-(2-methoxyethoxymethoxy)ethyl}amine,tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine,tris{2-(1-ethoxypropoxy)ethyl}amine,tris[2-{2-(2-hydroxyethoxy)ethoxy}ethyl]amine,4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane,4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane,1,4,10,13-tetraoxa-7,16-diazabicyclooctadecane, 1-aza-12-crown-4,1-aza-15-crown-5, 1-aza-18-crown-6, tris(2-formyloxyethyl)amine,tris(2-acetoxyethyl)amine, tris(2-propionyloxyethyl)amine,tris(2-butyryloxyethyl)amine, tris(2-isobutyryloxyethyl)amine,tris(2-valeryloxyethyl)amine, tris(2-pivaloyloxyethyl)amine,N,N-bis(2-acetoxyethyl)-2-(acetoxyacetoxy)ethylamine,tris(2-methoxycarbonyloxyethyl)amine,tris(2-tert-butoxycarbonyloxyethyl)amine,tris[2-(2-oxopropoxy)ethyl]amine,tris[2-(methoxycarbonylmethyl)oxyethyl]amine,tris[2-(tert-butoxycarbonylmethyloxy)ethyl]amine,tris[2-(cyclohexyloxycarbonylmethyloxy)ethyl]amine,tris(2-methoxycarbonylethyl)amine, tris(2-ethoxycarbonylethyl)amine,N,N-bis(2-hydroxyethyl)-2-(methoxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(methoxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-(ethoxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(ethoxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-(2-hydroxyethoxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(2-acetoxyethoxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-[(methoxycarbonyl)methoxycarbonyl]ethylamine,N,N-bis(2-acetoxyethyl)-2-[(methoxycarbonyl)methoxycarbonyl]ethylamine,N,N-bis(2-hydroxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)ethylamine,N,N-bis(2-acetoxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)ethylamine,N,N-bis(2-hydroxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxycarbonyl]ethylamine,N,N-bis(2-acetoxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxycarbonyl]ethylamine,N,N-bis(2-hydroxyethyl)-2-(4-hydroxybutoxycarbonyl)ethylamine,N,N-bis(2-formyloxyethyl)-2-(4-formyloxybutoxycarbonyl)ethylamine,N,N-bis(2-formyloxyethyl)-2-(2-formyloxyethoxycarbonyl)ethylamine,N,N-bis(2-methoxyethyl)-2-(methoxycarbonyl)ethylamine,N-(2-hydroxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine,N-(2-acetoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine,N-(2-hydroxyethyl)-bis[2-(ethoxycarbonyl)ethyl]amine,N-(2-acetoxyethyl)-bis[2-(ethoxycarbonyl)ethyl]amine,N-(3-hydroxy-1-propyl)-bis[2-(methoxycarbonyl)ethyl]amine,N-(3-acetoxy-1-propyl)-bis[2-(methoxycarbonyl)ethyl]amine,N-(2-methoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine,N-butyl-bis[2-(methoxycarbonyl)ethyl]amine,N-butyl-bis[2-(2-methoxyethoxycarbonyl)ethyl]amine,N-methyl-bis(2-acetoxyethyl)amine, N-ethyl-bis(2-acetoxyethyl)amine,N-methyl-bis(2-pivaloyloxyethyl)amine,N-ethyl-bis[2-(methoxycarbonyloxy)ethyl]amine,N-ethyl-bis[2-(tert-butoxycarbonyloxy)ethyl]amine,tris(methoxycarbonylmethyl)amine, tris(ethoxycarbonylmethyl)amine,N-butyl-bis(methoxycarbonylmethyl)amine,N-hexyl-bis(methoxycarbonylmethyl)amine, andβ-(diethylamino)-δ-valerolactone.

Also useful are basic compounds having cyclic structure, represented bythe following general formula (B)-2.

Herein X is as defined above, and R³⁰⁷ is a straight or branchedalkylene group of 2 to 20 carbon atoms which may contain one or morecarbonyl, ether, ester or sulfide groups.

Illustrative examples of the compounds having formula (B)-2 include1-[2-(methoxymethoxy)ethyl]pyrrolidine,1-[2-(methoxymethoxy)ethyl]piperidine,4-[2-(methoxymethoxy)ethyl]morpholine,1-[2-[(2-methoxyethoxy)methoxy]ethyl]pyrrolidine,1-[2-[(2-methoxyethoxy)methoxy]ethyl]piperidine,4-[2-[(2-methoxyethoxy)methoxy]ethyl]morpholine, 2-(1-pyrrolidinyl)ethylacetate, 2-piperidinoethyl acetate, 2-morpholinoethyl acetate,2-(1-pyrrolidinyl)ethyl formate, 2-piperidinoethyl propionate,2-morpholinoethyl acetoxyacetate, 2-(1-pyrrolidinyl)ethylmethoxyacetate, 4-[2-(methoxycarbonyloxy)ethyl]morpholine,1-[2-(t-butoxycarbonyloxy)ethyl]piperidine,4-[2-(2-methoxyethoxycarbonyloxy)ethyl]morpholine, methyl3-(1-pyrrolidinyl)propionate, methyl 3-piperidinopropionate, methyl3-morpholinopropionate, methyl 3-(thiomorpholino)propionate, methyl2-methyl-3-(1-pyrrolidinyl)propionate, ethyl 3-morpholinopropionate,methoxycarbonylmethyl 3-piperidinopropionate, 2-hydroxyethyl3-(1-pyrrolidinyl)propionate, 2-acetoxyethyl 3-morpholinopropionate,2-oxotetrahydrofuran-3-yl 3-(1-pyrrolidinyl)propionate,tetrahydrofurfuryl 3-morpholinopropionate, glycidyl3-piperidinopropionate, 2-methoxyethyl 3-morpholinopropionate,2-(2-methoxyethoxy)ethyl 3-(1-pyrrolidinyl)propionate, butyl3-morpholinopropionate, cyclohexyl 3-piperidinopropionate,α-(1-pyrrolidinyl)methyl-γ-butyrolactone, β-piperidino-γ-butyrolactone,β-morpholino-δ-valerolactone, methyl 1-pyrrolidinylacetate, methylpiperidinoacetate, methyl morpholinoacetate, methylthiomorpholinoacetate, ethyl 1-pyrrolidinylacetate, and 2-methoxyethylmorpholinoacetate.

Also, basic compounds having cyano group, represented by the followinggeneral formulae (B)-3 to (B)-6 are useful.

Herein, X, R³⁰⁷ and n are as defined above, and R³⁰⁸ and R³⁰⁹ are eachindependently a straight or branched alkylene group of 1 to 4 carbonatoms.

Illustrative examples of the basic compounds having cyano group,represented by formulae (B)-3 to (B)-6, include3-(diethylamino)propiononitrile,N,N-bis(2-hydroxyethyl)-3-aminopropiononitrile,N,N-bis(2-acetoxyethyl)-3-aminopropiononitrile,N,N-bis(2-formyloxyethyl)-3-aminopropiononitrile,N,N-bis(2-methoxyethyl)-3-aminopropiononitrile,N,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropiononitrile, methylN-(2-cyanoethyl)-N-(2-methoxyethyl)-3-aminopropionate, methylN-(2-cyanoethyl)-N-(2-hydroxyethyl)-3-aminopropionate, methylN-(2-acetoxyethyl)-N-(2-cyanoethyl)-3-aminopropionate,N-(2-cyanoethyl)-N-ethyl-3-aminopropiononitrile,N-(2-cyanoethyl)-N-(2-hydroxyethyl)-3-aminopropiononitrile,N-(2-acetoxyethyl)-N-(2-cyanoethyl)-3-aminopropiononitrile,N-(2-cyanoethyl)-N-(2-formyloxyethyl)-3-aminopropiononitrile,N-(2-cyanoethyl)-N-(2-methoxyethyl)-3-aminopropiononitrile,N-(2-cyanoethyl)-N-[2-(methoxymethoxy)ethyl]-3-aminopropiononitrile,N-(2-cyanoethyl)-N-(3-hydroxy-1-propyl)-3-aminopropiononitrile,N-(3-acetoxy-1-propyl)-N-(2-cyanoethyl)-3-aminopropiononitrile,N-(2-cyanoethyl)-N-(3-formyloxy-1-propyl)-3-aminopropiononitrile,N-(2-cyanoethyl)-N-tetrahydrofurfuryl-3-aminopropiononitrile,N,N-bis(2-cyanoethyl)-3-aminopropiononitrile, diethylaminoacetonitrile,N,N-bis(2-hydroxyethyl)aminoacetonitrile,N,N-bis(2-acetoxyethyl)aminoacetonitrile,N,N-bis(2-formyloxyethyl)aminoacetonitrile,N,N-bis(2-methoxyethyl)aminoacetonitrile,N,N-bis[2-(methoxymethoxy)ethyl]aminoacetonitrile, methylN-cyanomethyl-N-(2-methoxyethyl)-3-aminopropionate, methylN-cyanomethyl-N-(2-hydroxyethyl)-3-aminopropionate, methylN-(2-acetoxyethyl)-N-cyanomethyl-3-aminopropionate,N-cyanomethyl-N-(2-hydroxyethyl)aminoacetonitrile,N-(2-acetoxyethyl)-N-(cyanomethyl)aminoacetonitrile,N-cyanomethyl-N-(2-formyloxyethyl)aminoacetonitrile,N-cyanomethyl-N-(2-methoxyethyl)aminoacetonitrile,N-cyanomethyl-N-[2-(methoxymethoxy)ethyl]aminoacetonitrile,N-cyanomethyl-N-(3-hydroxy-1-propyl)aminoacetonitrile,N-(3-acetoxy-1-propyl)-N-(cyanomethyl)aminoacetonitrile,N-cyanomethyl-N-(3-formyloxy-1-propyl)aminoacetonitrile,N,N-bis(cyanomethyl)aminoacetonitrile, 1-pyrrolidinepropiononitrile,1-piperidinepropiononitrile, 4-morpholinepropiononitrile,1-pyrrolidineacetonitrile, 1-piperidineacetonitrile,4-morpholineacetonitrile, cyanomethyl 3-diethylaminopropionate,cyanomethyl N,N-bis(2-hydroxyethyl)-3-aminopropionate, cyanomethylN,N-bis(2-acetoxyethyl)-3-aminopropionate, cyanomethylN,N-bis(2-formyloxyethyl)-3-aminopropionate, cyanomethylN,N-bis(2-methoxyethyl)-3-aminopropionate, cyanomethylN,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropionate, 2-cyanoethyl3-diethylaminopropionate, 2-cyanoethylN,N-bis(2-hydroxyethyl)-3-aminopropionate, 2-cyanoethylN,N-bis(2-acetoxyethyl)-3-aminopropionate, 2-cyanoethylN,N-bis(2-formyloxyethyl)-3-aminopropionate, 2-cyanoethylN,N-bis(2-methoxyethyl)-3-aminopropionate, 2-cyanoethylN,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropionate, cyanomethyl1-pyrrolidinepropionate, cyanomethyl 1-piperidinepropionate, cyanomethyl4-morpholinepropionate, 2-cyanoethyl 1-pyrrolidinepropionate,2-cyanoethyl 1-piperidinepropionate, and 2-cyanoethyl4-morpholinepropionate.

The basic compound is preferably formulated in an amount of 0.001 to 2parts, and especially 0.01 to 1 part by weight, per 100 parts by weightof the base resin. Less than 0.001 phr of the basic compound achieves noor little addition effect whereas more than 2 phr would result in toolow a sensitivity.

Other Components

Also, a polymer comprising recurring units having amino and fluoroalkylgroups may be added. This polymer orients or segregates at the resistsurface after coating, preventing the resist pattern as developed fromslimming and improving rectangularity. For preventing pattern slimming,the addition of the following polymer is effective.

Herein R⁰¹, R⁰⁴, and R⁰⁷ are each independently hydrogen or methyl. X¹,Y¹ and Y² are each independently a single bond, —O—R⁰⁹—, —C(═O)—O—R⁰⁹—,—C(═O)—NH—R⁰⁹—, a straight or branched C₁-C₄ alkylene, or phenylenegroup, wherein R⁰⁹ is a straight, branched or cyclic C₁-C₁₀ alkylenegroup which may contain an ester (—COO—) or ether (—O—) group. Thesubscript n is 1 or 2. In case of n=1, Y¹ is a single bond, —O—R⁰⁹—,—C(═O)—O—R⁰⁹—, —C(═O)—NH—R⁰¹⁰—, a straight or branched C₁-C₄ alkylene,or phenylene group, wherein R⁰⁹ is as defined above. In case of n=2, Y¹is —O—R⁰¹⁰═, —C(═O)—O—R⁰¹⁰═, —C(═O)—NH—R⁰¹⁰═, a straight or branchedC₁-C₄ alkylene group with one hydrogen atom eliminated, or a phenylenegroup with one hydrogen atom eliminated, wherein R⁰¹⁰ is a straight,branched or cyclic C₁-C₁₀ alkylene group with one hydrogen atomeliminated which may contain an ester or ether group. R⁰² and R⁰³ areeach independently hydrogen, a straight, branched or cyclic C₁-C₂₀ alkylor C₂-C₂₀ alkenyl group which may contain a hydroxy, ether, ester,cyano, amino group, double bond or halogen atom, or a C₆-C₁₀ aryl group,or R⁰² and R⁰³ may bond together to form a ring of 3 to 20 carbon atomswith the nitrogen atom to which they are attached. R⁰⁵ is a straight,branched or cyclic C₁-C₁₂ alkylene group. R⁰⁶ is hydrogen, fluorine,methyl, trifluoromethyl or difluoromethyl, or R⁰⁶ and R⁰⁵ may bondtogether to form an alicyclic ring of 2 to 12 carbon atoms with thecarbon atom to which they are attached, which ring may contain an ethergroup, fluorinated alkylene group or trifluoromethyl group. R⁰⁸ is astraight, branched or cyclic C₁-C₂₀ alkyl group which has at least onefluorine atom substituted thereon and which may contain an ether, esteror sulfonamide group. The subscripts (a-1), (b-1), and (b-2) are numbersin the range: 0<(a-1)<1.0, 0≦(b-1)<1.0, 0≦(b-2)<1.0, 0<(b-1)+(b-2)<1.0,and 0.5≦(a-1)+(b-1)+(b-2)≦1.0.

In the positive resist composition, a compound having a group ≡C—COOH inthe molecule may be blended. Exemplary, non-limiting compounds having acarboxyl group include one or more compounds selected from Groups I andII below. Including this compound improves the post-exposure delay (PED)stability of the resist and ameliorates edge roughness on nitride filmsubstrates.

Group I:

Compounds of general formulas (A1) to (A10) below in which some or allof the hydrogen atoms on the phenolic hydroxyl groups have been replacedby —R⁴⁰¹—COOH (wherein R⁴⁰¹ is a straight or branched alkylene of 1 to10 carbon atoms), and in which the molar ratio C/(C+D) of phenolichydroxyl groups (C) to ≡C—COOH groups (D) in the molecule is from 0.1 to1.0.

In these formulas, R⁴⁰⁸ is hydrogen or methyl; R⁴⁰² and R⁴⁰³ are eachhydrogen or a straight or branched C₁-C₈ alkyl or alkenyl; R⁴⁰⁴ ishydrogen, a straight or branched C₁-C₈ alkyl or alkenyl, or a—(R⁴⁰⁹)_(h)—COOR′ group (R′ being hydrogen or —R⁴⁰⁹—COOH); R⁴⁰⁵ is—(CH₂)_(i)— (wherein i is 2 to 10), a C₆-C₁₀ arylene, carbonyl,sulfonyl, an oxygen atom, or a sulfur atom; R⁴⁰⁶ is a C₁-C₁₀ alkylene, aC₆-C₁₀ arylene, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom;R⁴⁰⁹ is hydrogen, a straight or branched C₁-C₈ alkyl or alkenyl, or ahydroxyl-substituted phenyl or naphthyl; R⁴⁰⁹ is a straight or branchedC₁-C₁₀ alkyl or alkenyl or a —R⁴¹¹—COOH group; R⁴¹⁰ is hydrogen, astraight or branched C₁-C₈ alkyl or alkenyl, or a —R⁴¹¹—COOH group; R⁴¹¹is a straight or branched C₁-C₁₀ alkylene; h is an integer of 1 to 4, jis an integer from 0 to 3; s1, t1, s2, t2, s3, t3, s4, and t4 are eachnumbers which satisfy s1+t1=8, s2+t2=5, s3+t3=4, and s4+t4=6, and aresuch that each phenyl structure has at least one hydroxyl group; u is aninteger of 1 to 4; κ is a number such that the compound of formula (A6)may have a weight average molecular weight of 1,000 to 5,000; and λ is anumber such that the compound of formula (A7) may have a weight averagemolecular weight of 1,000 to 10,000.

Group II:

Compounds of general formulas (A11) to (A15) below.

In these formulas, R⁴⁰², R⁴⁰³, and R⁴¹¹ are as defined above; R⁴¹² ishydrogen or hydroxyl; s5 and t5 are numbers which satisfy s5≧0, t5≧0,and s5+t5=5; and h′ is 0 or 1.

Illustrative, non-limiting examples of the compound having a carboxylgroup include compounds of the general formulas (AI-1) to (AI-14) and(AII-1) to (AII-10) below.

In the above formulas, R″ is hydrogen or a —CH₂COOH group such that the—CH₂COOH group accounts for 10 to 100 mol % of R″ in each compound, κand λ are as defined above.

The carboxyl compound is added in an amount ranging from 0 to 5 parts,preferably 0.1 to 5 parts, more preferably 0.1 to 3 parts, furtherpreferably 0.1 to 2 parts by weight, per 100 parts by weight of the baseresin. More than 5 phr of the compound may reduce the resolution of theresist composition.

The positive resist composition used herein may further include asurfactant for improving the coating characteristics.

Illustrative, non-limiting, examples of the surfactant include nonionicsurfactants, for example, polyoxyethylene alkyl ethers such aspolyoxyethylene lauryl ether, polyoxyethylene stearyl ether,polyoxyethylene cetyl ether, and polyoxyethylene oleyl ether,polyoxyethylene alkylaryl ethers such as polyoxyethylene octylphenolether and polyoxyethylene nonylphenol ether, polyoxyethylenepolyoxypropylene block copolymers, sorbitan fatty acid esters such assorbitan monolaurate, sorbitan monopalmitate, and sorbitan monostearate,and polyoxyethylene sorbitan fatty acid esters such as polyoxyethylenesorbitan monolaurate, polyoxyethylene sorbitan monopalmitate,polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitantrioleate, and polyoxyethylene sorbitan tristearate; fluorochemicalsurfactants such as EFTOP EF301, EF303 and EF352 (Tohkem Products Co.,Ltd.), Megaface F171, F172 and F173 (Dai-Nippon Ink & Chemicals, Inc.),Fluorad FC-430, FC-431 and FC-4430 (Sumitomo 3M Co., Ltd.), AsahiguardAG710, Surflon S-381, S-382, SC101, SC102, SC103, SC104, SC105, SC106,Surfynol E1004, KH-10, KH-20, KH-30 and KH-40 (Asahi Glass Co., Ltd.);organosiloxane polymers KP-341, X-70-092 and X-70-093 (Shin-EtsuChemical Co., Ltd.), acrylic acid or methacrylic acid Polyflow No. 75and No. 95 (Kyoeisha Ushi Kagaku Kogyo Co., Ltd.). Inter alia, FC-430,FC-4430, Surflon S-381, Surfynol E1004, KH-20 and KH-30 are preferred.These surfactants may be used alone or in admixture.

To the positive resist composition, the surfactant is added in an amountof up to 2 parts, preferably up to 1 part by weight, per 100 parts byweight of the base resin.

Second Resist Composition

The second positive resist composition from which a second resist filmserving as a reversal film in the double pattern forming process of theinvention is formed comprises as a base resin a polymer comprisingrecurring units having an alkali-soluble group protected with an acidlabile group which is eliminatable with acid. Preferably the polymercomprises recurring units having a lactone ring and recurring unitshaving an alkali-soluble group protected with an acid labile group whichis eliminatable with acid. More preferably the recurring units having analkali-soluble group protected with an acid labile group which iseliminatable with acid are recurring units of the general formula (c):

wherein R⁸ is hydrogen or methyl, R⁹ is an acid labile group, and c is anumber in the range: 0<c≦0.8.

The monomers from which recurring units of formula (c) are derived aremonomers Mc of the following formula wherein R⁸ and R⁹ are as definedabove.

The acid labile group represented by R⁹ in formula (c) may be selectedfrom a variety of such groups, specifically groups of formulae (AL-10)and (AL-11), tertiary alkyl groups of formula (AL-12), and oxoalkylgroups of 4 to 20 carbon atoms, as previously illustrated for the acidlabile groups in the first resist composition. Exemplary acid labilegroups are the same as exemplified previously.

While the polymer used in the second positive resist compositionpreferably includes recurring units of formula (c), it may havecopolymerized therein recurring units (d) derived from monomers havingadhesive groups such as hydroxy, cyano, carbonyl, ester, ether groups,lactone rings, carbonyl groups or carboxylic anhydride groups. Examplesof recurring units (d) are the same as exemplified previously inconnection with the first positive resist composition.

In the polymer, the recurring units (c) and (d) are present inproportions c and d, respectively, which satisfy the range: 0<c≦0.8 and0≦d<1.0, and preferably 0.1≦c≦0.7 and 0≦d≦0.9, provided that c+d=1.

It is noted that the meaning of c+d=1 is that in a polymer comprisingrecurring units (c) and (d), the sum of recurring units (c) and (d) is100 mol % based on the total amount of entire recurring units.

The base resin in the second positive resist composition from which asecond resist film serving as a reversal film in the double patternforming process of the invention is formed may also include phenolicpolymers as used in KrF, EB and EUV lithography processes. A number ofresist materials comprising phenolic polymers have been proposed. Usemay be made of the resist materials described in the following patentreferences.

JP-A 10-207066 JP-A 10-020504 JP-A 10-265524 JP-A 2001-324814 JP-A2002-202610 JP-A 2002-234910 JP-A 2002-244297 JP-A 2002-107934 JP-A2002-107933 JP-A 2003-84440 JP-A 2003-131384 JP-A 2004-45448 JP-A2004-61794 JP-A 2004-115630 JP-A 2004-149756 JP-A 2004-348014 JP-A2005-8766 JP-A 2005-8769 JP-A 2006-169302 JP-A 2007-114728 JP-A2007-132998 JP-A 2007-254494 JP-A 2007-254495 JP-A 2007-270128 JP-A2008-50568 JP-A 2008-95009

The polymer serving as the base resin in the second resist material usedin the double pattern forming process of the invention should preferablyhave a weight average molecular weight (Mw) in the range of 2,000 to30,000, as measured by gel permeation chromatography (GPC) usingpolystyrene standards. A polymer with too low a Mw may allow forsubstantial acid diffusion during PEB, leading to degraded resolution.With too high a Mw, it may be difficult to embed the second resistmaterial close between features of the first resist pattern, and thepolymer may lose alkali solubility and give rise to a footing phenomenonafter pattern formation.

If a polymer used in the second resist material (like the polymer in thefirst resist material) has a wide molecular weight distribution ordispersity (Mw/Mn), which indicates the presence of lower and highermolecular weight polymer fractions, there is a possibility that foreignmatter is left on the pattern or the pattern profile is degraded. Theinfluences of molecular weight and dispersity become stronger as thepattern rule becomes finer. Therefore, the multi-component copolymershould preferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0,especially 1.0 to 1.5, in order to provide a resist composition suitablefor micropatterning to a small feature size.

It is understood that a blend of two or more polymers which differ incompositional ratio, molecular weight or dispersity is acceptable.

The polymer as used herein may be synthesized by any desired method, forexample, by dissolving unsaturated bond-containing monomerscorresponding to the respective units (c) and (d) in an organic solvent,adding a radical initiator thereto, and effecting heat polymerization.Examples of the organic solvent which can be used for polymerizationinclude toluene, benzene, tetrahydrofuran, diethyl ether and dioxane.Examples of the polymerization initiator used herein include2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is 2 to 100 hours, preferably 5 to 20hours. The acid labile group that has been incorporated in the monomersmay be kept as such, or the acid labile group may be once removed withan acid catalyst and thereafter protected or partially protected.

The base resin in the second positive resist composition used in thedouble pattern forming process of the invention may also includepolysiloxane compounds, specifically polysiloxane compounds comprisingstructural units having the general formulae (1) and (2) and furthercomprising third structural units having the general formula (3).

Herein R¹⁰ is a C₃-C₂₀ monovalent organic group of straight, branched,cyclic or polycyclic structure which has a hydroxyl group on a carbonatom as a functional group, which has in total at least three fluorineatoms substituted on carbon atoms bonded to the hydroxyl-bonded carbonatom, and which may contain one or more halogen, oxygen or sulfur atomin addition to the fluorine atoms. R¹ is a C₁-C₆ monovalent hydrocarbongroup of straight, branched or cyclic structure. R¹² is a C₃-C₂₀monovalent organic group of straight, branched, cyclic or polycyclicstructure which has a carboxyl group protected with an acid labileprotective group as a functional group, and which may contain one ormore halogen, oxygen or sulfur atom in addition to the carboxyl group.R¹³ is as defined for R¹¹. R¹⁴ is a C₄-C₁₆ monovalent organic groupwhich has a lactone ring as a functional group and which may contain oneor more halogen, oxygen or sulfur atom in addition to the lactone ring.R¹⁵ is as defined for R¹¹. The subscript p is 0 or 1, q is 0 or 1, and ris 0 or 1.

The unit having formula (1) is incorporated as a structural unit havinga polar group capable of controlling swell. It contributes to thiseffect that unlike ordinary alcohols, the hydroxyl group on R¹⁰ affordsan adequate acidity because the density of electrons on oxygen isreduced due to the strong attraction of electrons by fluorine atomsbonded at adjacent positions. Fluorine atoms exert a substantialelectron attracting effect when they are bonded to a carbon atom whichis bonded to the hydroxyl-bonded carbon atom, but less such effect whenbonded at a remoter position. To acquire this effect more efficiently,it is preferred to attach a trifluoromethyl group(s) to thehydroxyl-bonded carbon atom. A typical partial structure ishexafluoroisopropyl group. A number of such fluorine-substituted alcoholderivatives have already been reported. A silicone structural unit canbe obtained by effecting hydrosilylation between such an alcoholderivative having an unsaturated bond and a silane to form a silanemonomer, followed by hydrolytic condensation. The skeleton ofsubstituent group forming the side chain is a C₃-C₂₀ organic group ofstraight, branched, cyclic or polycyclic structure which may contain ahalogen, oxygen or sulfur atom(s). Several of fluorinated siliconecompounds having a hydroxyl group have already been disclosed (e.g., inJP-A 2002-268227 and JP-A 2003-173027) and they all can be generallyused herein. Of the structural units belonging to this genus, a choiceof a single unit may be made or a mixture of two or more different unitsmay be used. Of these units, use of a structural unit having anorbornane skeleton is advantageous in purification or the like becausethe resulting resin is most likely solid. Some typical examples aregiven below.

Of the structural units having formula (1), polysiloxane compoundshaving the following formula (Si-10) are preferred.

In the structural unit having formula (2), R¹² is a side chain havingcarboxylic acid protected with an acid labile group, which functions toestablish differential dissolution between exposed and unexposed areas.The acid labile group is a technical term generally used in theresist-related art. The acid labile group with which a functional groupis protected functions such that when a strong acid is generated from aphotoacid generator upon exposure, the bond between the acid labilegroup and the functional group is scissored under the catalysis of thestrong acid. As a result of scission, carboxylic acid is regeneratedherein. The protective group used herein may be any of well-knowngroups. When carboxylic acid is to be protected, the preferredprotective groups are C₄-C₂₀ tertiary alkyl groups, C₃-C₁₈ trialkylsilylgroups, and C₄-C₂₀ oxoalkyl groups. Of the tertiary alkyl groups, thosetertiary alkyl groups in which substituent groups on a tertiary carbonatom are substituted so as to form a 5- to 7-membered ring with thattertiary carbon and those tertiary alkyl groups in which a carbon chainbonded to a tertiary carbon atom has a branched or cyclic structure aremost preferred because they afford high resolution.

The side chain bearing carboxylic acid to be protected is a C₃-C₂₀organic group of straight, branched, cyclic or polycyclic structurewhich may contain a halogen, oxygen or sulfur atom(s). As in theprevious case, this is also readily obtainable by effectinghydrosilylation of a protected carboxylic acid derivative having anunsaturated carbon bond with a silane to form a silicone monomer,followed by hydrolytic condensation. Of these, those monomers in whichboth silicon and a protected carboxyl group are in direct bond with anorbornane ring or tetracyclododecene ring are most preferred becausethey afford high resolution. Of the structural units having formula (2),those having the following formula (Si-11) are preferred.

Herein R¹⁶ is an acid labile group, and n is an integer of 0 or 1.

Preferred examples of the acid labile group represented by R¹⁶ are givenbelow.

Like the unit of formula (1), for the unit of formula (2), a single unitor a mixture of different units belonging to this genus may be used.

The unit of formula (3) ensures that the silicone resin has a necessarypolarity and serves as a second polar group functioning to reduce thenecessary quantity of the unit of formula (2). With respect to the polargroup, a number of polar groups including hydroxy, carbonyloxyalkyl,carboxyl and carbonate groups have already been disclosed. An actualattempt to combine the unit of formula (1) with the unit of formula (2)failed to provide such an effect as exerted by acrylic acid polymers forthe single layer use, that is, failed to provide high resolution. Bycontrast, the additional use of the lactone skeleton-bearing unit havingformula (3) is successful in establishing both polarity and highresolution.

The silicone structure having a lactone skeleton which have beenreported include those structures having lactone incorporated in acyclic structure, those structures having a linker, and those structuresin which lactone is linked to a cyclic structure via a linker (see JP-A2002-268227). Of these, the structural units having a cycloaliphaticskeleton and further a five-membered lactone skeleton bonded thereto,and having a side chain in which a silicon atom is bonded to one ofcarbon atoms within the cycloaliphatic skeleton are most preferredbecause the highest resolution is accomplished.

Two structural units (i.e., silicone side chains) affording the bestresolution are illustrated below.

Herein Y is an oxygen atom, sulfur atom or methylene group, and m is 0or 1.

Of the above-illustrated compounds of formula (Si-12), those side chainswherein Y is oxygen are more preferred for use in the inventivecomposition because of a more polar effect. Of the above-illustratedcompounds of formula (Si-13), those compounds wherein m is 0 and thosecompounds wherein m is 1 may be used alone or in admixture.

Like the units of formulae (1) and (2), for the unit of formula (3), asingle unit or a mixture of different units belonging to this genus maybe used.

The structural units having formulae (1), (2) and (3) may be eitherdivalent structural units or trivalent silicone compounds. The situationwhere p, q or r is 0 means trivalent and the situation where p, q or ris 1 means divalent. When divalent structural units account for 50 mol %or more based on the entire structural units of formulae (1), (2) and(3), a silicone resin resulting from condensation of these monomers isunlikely to solidify and thus difficult to purify. Thus, trivalentstructural units are preferably included in an amount of at least 50 mol%.

When the divalent monomer is used, the other side chain R¹¹, R¹³ or R¹⁵from silicon may be selected from simple groups because no particularfunction is assigned thereto. Since a carbon number in excess of 6 tendsto interfere with purification by distillation or the like, a choice ispreferably made of hydrocarbon groups having not more than 6 carbonatoms.

With respect to the proportion of structural units having formulae (1),(2) and (3), first of all, the ratio of the structural unit of formula(2) to the entire silicone structural units is determined because adissolution contrast between exposed and unexposed areas of a resistcoating is almost dictated by this ratio. The ratio of the structuralunit of formula (2) is preferably 5 to 80 mol %, more preferably 10 to50 mol %, based on the entire polysiloxane compound although it variessomewhat with the molecular weight of the protecting group or the like.

Next, the total amount of polar groups, that is, the total amount of thestructural units of formulae (1) and (3) is preferably 20 to 95 mol %,more preferably 50 to 90 mol %, based on the entire polysiloxanecompound. If these units are in short, the resist pattern can collapseby peeling and swelling during development. If these units are inexcess, the resist coating may have a lower contrast and lowerresolution.

With respect to the ratio of the structural unit of formula (1) to thestructural unit of formula (3), if one structural unit is less than 10mol % based on the total of these two structural units, the function ofthe one structural unit is not available. It is thus preferred that eachstructural unit be 10 to 90 mol % based on the total of structural unitsof formulae (1) and (3).

Further, divalent or more siloxane units other than the structural unitsof formulae (1) to (3) may be added as long as their amount is at most30 mol % of the entire polysiloxane compound. For example, where everysiloxane structural unit has a bulky side chain, in some cases, only acompound with a lower molecular weight can be obtained through mereadjustment of condensation conditions for polysiloxane synthesis. Insuch cases, the molecular weight can be increased by adding units havingonly an alkyl group of at most 4 carbon atoms, typically methylsiloxane.Also, where it is desired to enhance the transparency of a resin toexposure light of shorter wavelength, typically light of 157 nm, it isknown effective to increase the number of fluorine atoms contained inthe resin per unit weight. For imparting such transparency to the resistof the invention, it is effective to introduce siloxane units havingfluoroalkyl groups introduced therein.

These siloxane structure units can be synthesized by cohydrolyticcondensation of a mixture of hydrolyzable silane compounds correspondingto the respective units, i.e., by contacting a mixture of silanemonomers with water. The reaction may be effected in the presence of anacid catalyst or base catalyst and also in an organic solvent. Examplesof suitable acid catalysts used in the reaction include hydrochloricacid, nitric acid, acetic acid, oxalic acid, sulfuric acid,methanesulfonic acid, p-toluenesulfonic acid, trifluoroacetic acid,trifluoromethanesulfonic acid, perchloric acid, phosphoric acid andcitric acid. Examples of suitable base catalysts include ammonia,methylamine, dimethylamine, ethylamine, diethylamine, triethylamine,sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide,tetrapropylammonium hydroxide, choline, diethylhydroxylamine, DBU, andDBN. Suitable organic solvents include polar solvents such as ethanol,IPA, MIBK, acetonitrile, DMA, and DMF, and aromatic solvents such asbenzene, toluene, and xylene, which may be used alone or in admixture.

The silicone resin or polysiloxane compound produced as the cohydrolyticcondensate of a mixture of silane monomers should preferably have aweight average molecular weight (Mw) of 1,000 to 100,000, morepreferably 1,000 to 30,000, and even more preferably 1,500 to 20,000, asmeasured by GPC versus polystyrene standards. Resins having a Mw inexcess of 100,000 may be difficult to purify, resins having a Mw inexcess of 30,000 tend to decline in resolution, though depending on acombination of monomers, and resins having a Mw in excess of 20,000 mayhave similar tendency. Resins having a Mw of less than 1,500 tend tohave a rounded pattern profile, and resins having a Mw of less than1,000 may have more tendency. During subsequent etching of theunderlying film, such a rounded pattern profile can cause to preventperpendicular etching of the film.

The second resist composition used in the double pattern forming processof the invention and comprising a polysiloxane compound as a base resinmay further comprise an organic solvent, a compound capable ofgenerating an acid in response to high-energy radiation (known as “acidgenerator”), and optionally, a dissolution inhibitor, a basic compound,a surfactant, and other components. These components including organicsolvent, acid generator, dissolution inhibitor, basic compound, andsurfactant are previously described in conjunction with the first resistcomposition and their examples are also the same as previouslyillustrated. Since the second resist material does not have therequirements of crosslinking reaction to acquire organic solventresistance and positive elimination of acid labile groups for conversionto alkali solubility, addition of a thermal acid generator may beomitted. In the embodiment wherein the second resist composition used inthe double pattern forming process comprises a polysiloxane compound asa base resin, a polysiloxane compound having a higher silicon content isdesirable. Where other additives are organic compounds so that theoverall resist composition may have a lower silicon content, it ispreferred to reduce the amounts of organic compounds.

The resist material for forming a second resist pattern is preferablytailored such that a surface layer of the second resist film may have ahigher rate of alkaline dissolution because reversal of the first resistpattern takes place smoothly. Enhancing the alkali solubility of only asurface layer of the pattern reversal film is advantageous for allowingfor smooth dissolution of the pattern reversal film building up over thepositive resist pattern which has been altered to be alkali soluble, andfor enhancing the dimensional control of a trench pattern or holepattern converted from the positive pattern. To enhance the surfacealkali solubility, an alkali soluble surfactant, especiallyfluorochemical surfactant may be added. The preferred fluorochemicalsurfactants are those comprising either one or both of recurring units(s-1) and (s-2) represented by the general formula (4).

Herein, R^(s6) and R^(s9) are each independently hydrogen or methyl. Theletter ns is equal to 1 or 2. In case of ns=1, X_(s1) is a phenylenegroup, —O—, —C(═O)—O—R^(s12)—, or —C(═O)—NH—R^(s12)— wherein R^(s12) isa single bond or a straight or branched C₁-C₄ alkylene group which mayhave an ester (—COO—) or ether (—O—) group. In case of ns=2, X_(s1) is aphenylene group with one hydrogen atom eliminated, or —C(═O)—O—R^(s81)═or —C(═O)—NH—R^(s81)═ wherein R^(s81) is a straight, branched or cyclicC₁-C₁₀ alkylene group with one hydrogen atom eliminated, which may havean ester or ether group. R^(s7) is a single bond or a straight, branchedor cyclic C₁-C₁₂ alkylene group. R^(s8) is hydrogen, fluorine, methyl,trifluoromethyl or difluoromethyl, or R^(s8) and R^(s7) may bondtogether to form a ring of 3 to 10 carbon atoms (exclusive of aromaticring) with the carbon atom to which they are attached, which ring mayhave an ether group, fluorinated alkylene group or trifluoromethylgroup. X_(s2) is a phenylene group, —O—, —C(═O)—O—R^(s11)—, or—C(═O)—N—-R^(s11)— wherein R^(s11) is a single bond or a straight orbranched C₁-C₄ alkylene group which may have an ester or ether group.R^(s10) is a fluorine atom or a straight, branched or cyclic C₁-C₂₀alkyl group, which may be substituted with at least one fluorine atomand which may have an ether, ester or sulfonamide group. The letter msis an integer of 1 to 5 when X_(s2) is phenylene, and ms is 1 whenX_(s2) is otherwise.

Examples of the monomers from which units (s-1) are derived include theabove described examples of the monomers from which the recurring unitssubstituted with acid labile groups of formula (AL-12)-20 are derived aswell as the following.

Herein R^(s6) is as defined above.

Examples of the monomers from which recurring units (s-2) in formula (4)are derived are illustrated below while many recurring units (s-2) areunits having a fluorinated alkyl group.

Herein R^(s9) is as defined above.

A total proportion of recurring units (s-1) and (s-2) is preferably 30to 100 mol %, and more preferably 50 to 100 mol % of the fluorochemicalsurfactant.

These recurring units (s-1) and (s-2) may be copolymerized with theabove-described alkali soluble recurring units having a phenol orcarboxyl group or substantially alkali insoluble recurring units.

The alkali soluble surfactant is preferably added in an amount of 0 to50 parts, and more preferably 0 to 20 parts by weight per 100 parts byweight of the base polymer. Too much amounts of the surfactant may causeexcessive slimming or detract from etching resistance. When added, atleast 1 phr of the surfactant is preferred.

Process

Now referring to the drawings, the double patterning process of theinvention is illustrated. The first positive resist composition iscoated on a substrate to form a first resist film thereon. As shown inFIG. 1, state (A), a first resist film 30 of a positive resistcomposition is formed on a processable substrate 20 disposed on asubstrate 10 directly or via an intermediate intervening layer (notshown). The first resist film preferably has a thickness of 10 to 1,000nm and more preferably 20 to 500 nm. Prior to exposure, the resist filmis heated or prebaked, preferably at a temperature of 60 to 180° C.,especially 70 to 150° C., even more preferably 80 to 120° C. for a timeof 10 to 300 seconds, especially 15 to 200 seconds, even more preferably30 to 120 seconds.

The substrate 10 used herein is generally a silicon substrate. Theprocessable substrate 20 used herein includes SiO₂, SiN, SiON, SiOC,p-Si, α-Si, TiN, WSi, BPSG, SOG, Cr, CrO, CrON, MoSi, low dielectricconstant film, and etch stopper film. The intermediate intervening layerincludes hard masks of SiO₂, SiN, SiON or p-Si, an undercoat in the formof carbon film, a silicon-containing intermediate film, and an organicantireflective coating.

Preferably, a carbon film containing at least 75% by weight of carbon isdisposed on the processable substrate, and a silicon-containingintermediate layer and a photoresist film are sequentially disposedthereon. Alternatively, a carbon film containing at least 75% by weightof carbon is disposed on the processable substrate, and a hard mask ofSiO₂, SiN, SiON or p-Si, an organic antireflective coating (BARC), and aphotoresist film are sequentially disposed thereon.

Where the second resist composition used in the double patterningprocess of the invention is a resist composition comprising apolysiloxane compound as defined above, the lower layer of the doublepattern formed on the processable substrate is preferably made of anorganic film-forming material so that the double pattern may be used asthe so-called bilayer resist.

Where the double pattern is used as a bilayer resist, the organicfilm-forming material of which the lower layer of the double patternformed on the processable substrate is made may be selected from manywell-known materials. The organic film is briefly described. Basically,aromatic resins are preferred. More preferred are those resins which arecrosslinked upon film formation so that intermixing may not occur whenthe resist composition is subsequently coated to form a film thereon.

Suitable aromatic resins include novolac resins and polyhydroxystyreneresins, and those resins having a fluorene or indene framework may beadvantageously used in order to enhance the etch resistance of thisorganic film during etching of the substrate after pattern transfer tothis organic film. Also an ARC may be formed on the organic film and aresist film according to the invention be formed thereon. The organicfilm having an antireflection function is preferred because the processbecomes more simple. For such an antireflection function, it ispreferred to use a resin having an anthracene or naphthalene frameworkor a benzene framework with conjugated unsaturated bond.

Crosslinks may be formed using thermosetting resins or a crosslinkingtechnique employed in negative resist compositions. One common methoduses a composition in solution form comprising a resin having functionalgroups such as phenol, alkoxyphenyl, alcohol or carboxylic acid, asubstance capable of generating an acid through thermal decomposition,and a crosslinker (e.g., hexaalkoxymethylmelamine) capable of formingcrosslinks with the functional groups in the presence of an acidcatalyst. The composition is coated onto a processable substrate andheated to generate the acid whereby crosslinks are formed.

Then the first resist composition is exposed. For the exposure,preference is given to high-energy radiation having a wavelength of 140to 250 nm, and especially ArF excimer laser radiation of 193 nm. Theexposure may be done either in air or in a dry atmosphere with anitrogen stream, or by immersion lithography in water. The ArF immersionlithography uses deionized water or liquids having a refractive index ofat least 1 and highly transparent to the exposure wavelength such asalkanes as the immersion solvent. The immersion lithography involvesprebaking a resist film and exposing the resist film to light through aprojection lens, with water introduced between the resist film and theprojection lens. Since this allows lenses to be designed to a NA of 1.0or higher, formation of finer feature size patterns is possible. Theimmersion lithography is important for the ArF lithography to survive tothe 45-nm node. In the case of immersion lithography, deionized waterrinsing (or post-soaking) may be carried out after exposure for removingwater droplets left on the resist film, or a protective film may beapplied onto the resist film after pre-baking for preventing anyleach-out from the resist film and improving water slip on the filmsurface. The resist protective film used in the immersion lithography ispreferably formed from a solution of a polymer having1,1,1,3,3,3-hexafluoro-2-propanol residues which is insoluble in water,but soluble in an alkaline developer liquid, in a solvent selected fromalcohols of at least 4 carbon atoms, ethers of 8 to 12 carbon atoms, andmixtures thereof. After formation of the photoresist film, deionizedwater rinsing (or post-soaking) may be carried out for extracting theacid generator and the like from the film surface or washing awayparticles, or after exposure, rinsing (or post-soaking) may be carriedout for removing water droplets left on the resist film.

Exposure is preferably carried out so as to provide an exposure dose ofabout 1 to 200 mJ/cm², more preferably about 10 to 100 mJ/cm², and evenmore preferably 10 to 50 mJ/cm². This is followed by baking on a hotplate at 60 to 150° C. for 30 seconds to 5 minutes, preferably at 80 to120° C. for 30 seconds to 3 minutes (post-exposure baking=PEB).

Thereafter the first resist film is developed with a developer in theform of an aqueous alkaline solution, for example, an aqueous solutionof 0.1 to 5 wt %, preferably 2 to 3 wt % tetramethylammonium hydroxide(TMAH) for 0.1 to 3 minutes, preferably 0.5 to 2 minutes by conventionaltechniques such as dip, puddle or spray techniques. In this way, adesired resist pattern 30 a is formed on the substrate as shown in FIG.2, state (B).

The line pattern of the first resist film resulting from the abovepatterning process is removed, leaving a space pattern in a secondresist film to which it is reversal transferred. When the space patternto be reversal transferred to the second resist film is finished thin,such thin finish can be achieved by increasing the exposure dose ofhigh-energy radiation applied in forming pattern 30 a of the firstresist film. FIG. 3, state (B-1) shows an exemplary pattern having aline size reduced by over-exposure of the first resist film.

Next, the first resist pattern is treated so as to eliminate acid labilegroups in the polymer and to crosslink the polymer, forming acrosslinked pattern 30 b as shown in FIG. 4, state (C). To induceelimination of acid labile groups and crosslinking to the polymer in thefirst resist pattern, acid and heat are necessary. In practice, an acidis generated, after which heat is applied to effect elimination of acidlabile groups and crosslinking at the same time.

The acid may be generated by a suitable method such as flood exposure ofthe wafer (pattern) as developed for decomposing the photoacidgenerator. The flood exposure uses an exposure wavelength of 180 to 400nm and an exposure dose of 10 mJ/cm² to 1 J/cm². Radiation with awavelength of less than 180 nm, specifically irradiation of excimerlasers of 172 nm, 146 nm and 122 nm or excimer lamps is undesirablebecause not only the generation of acid from photoacid generator, butalso photo-induced crosslinking reaction are accelerated, leading to adecrease of alkaline dissolution rate due to excessive crosslinking. Forthe flood exposure, use is preferably made of an ArF excimer laser witha wavelength longer than 193 nm, a KrCl excimer lamp of 222 nm, a KrFexcimer laser of 248 nm, a low-pressure mercury lamp centering at 254nm, a XeCl excimer lamp of 308 nm, and i-line of 365 nm.

However, it is desired to avoid the use of an equipment for floodexposure because the equipment itself is expensive and because of thedisadvantage that if it is built in the semiconductor device productionline, the throughput of the line is reduced by an increased number ofsteps.

As mentioned above, in the step of treating the first resist pattern toeliminate acid labile groups in the polymer and to crosslink the polymerto form a crosslinked pattern 30 b as shown in FIG. 4, state (C), acidand heat are necessary for elimination and crosslinking. To positivelygenerate an acid, a thermal acid generator may be added to the firstresist composition.

In the embodiment wherein a thermal acid generator in the form of anammonium salt is added to the positive resist composition, an acid canbe generated by heating. In this embodiment, acid generation andcrosslinking reaction take place simultaneously. Preferred heatingconditions include a temperature of 180 to 220° C. and a time of 10 to300 seconds, especially 30 to 60 seconds. As a result, a crosslinkedresist pattern which is insoluble in the solvent of the second resistcomposition or reversal film-forming composition is yielded.

Suitable ammonium salts serving as the thermal acid generator includecompounds of the formula (P1a-2). The addition of a thermal acidgenerator to the first resist composition is advantageous in that ithelps the first resist film to exhibit alkali solubility and it promotescrosslinking reaction to impart resistance to the organic solvent usedin coating of a second resist film. However, excess addition of athermal acid generator gives rise to some problems. The thermal acidgenerator may be added in such amounts as to provide no impact on thelithography of patterning the first resist film, no impact on thethermal properties of the first resist film, and no impact on the secondresist film. Specifically, the thermal acid generator may be added in anamount of up to 5%, preferably up to 3%, and more preferably 0.01 to 1%by weight based on the weight of the base resin in the first resistfilm.

Herein K⁻ is a sulfonate having at least one fluorine substituted atα-position, or perfluoroalkylimidate or perfluoroalkylmethidate.R^(101d), R^(101e), R^(101f), and R^(101g) are each independentlyhydrogen, a straight, branched or cyclic alkyl, alkenyl, oxoalkyl oroxoalkenyl group of 1 to 12 carbon atoms, an aryl group of 6 to 20carbon atoms, or an aralkyl or aryloxoalkyl group of 7 to 12 carbonatoms, in which some or all hydrogen atoms may be substituted by alkoxygroups. Alternatively, R^(101d) and R^(101e), or R^(101d), R^(101e) andR^(101f) may bond together to form a ring with the nitrogen atom towhich they are attached, and each of R^(101e) and R^(101f) or each ofR^(101d), R^(101e) and R^(101f) is a C₃-C₁₀ alkylene group or ahetero-aromatic ring having incorporated therein the nitrogen atom whenthey form a ring.

Examples of K⁻ include perfluoroalkanesulfonates such as triflate andnonaflate, imidates such as bis(trifluoromethylsulfonyl)imide,bis(perfluoroethylsulfonyl)imide, and bis(perfluorobutylsulfonyl)imide,methidates such as tris(trifluoromethylsulfonyl)methide andtris(perfluoroethylsulfonyl)methide, and sulfonates having fluorinesubstituted at α-position, represented by the formula (K-1), andsulfonates having fluorine substituted at α-position, represented by theformula (K-2).

In formula (K-1), R^(102a) is hydrogen, a straight, branched or cyclicC₁-C₂₀ alkyl or acyl group, C₂-C₂₀ alkenyl group or C₆-C₂₀ aryl oraryloxy group, which may have an ether, ester, carbonyl group or lactonering and in which some or all hydrogen atoms may be substituted byfluorine atoms. In formula (K-2), R^(102b) is hydrogen, a straight,branched or cyclic C₁-C₂₀ alkyl group, C₂-C₂₀ alkenyl group or C₆-C₂₀aryl group.

Apart from the embodiment of performing flood exposure and theembodiment of adding a thermal acid generator to positively generate anacid in the first resist pattern, there is a possible embodiment whereina minor amount of residual acid which has diffused from the exposed areaand remains in the first resist pattern react with acid labile groups atelevated temperature whereby the acid labile groups are eliminated sothat the first positive resist pattern turns to be alkali soluble, andcrosslinking reaction take place under the action of that acid and heatso that the pattern is endowed with solvent resistance. It has beenobserved that some acid labile groups are thermally eliminated byheating at high temperature. It has also been observed that the firstresist pattern is converted from a positive behavior to be insoluble inalkaline developer to an alkaline developer soluble behavior by heatingat high temperature. As long as the first resist composition accordingto the invention is used, acid-assisted elimination of acid labilegroups for the first resist pattern to convert from alkaline developerinsolubility to solubility and impartment of resistance to organicsolvent in the second resist composition for reversal transfer can beaccomplished simply by heating at high temperature. In the step ofheating at high temperature to facilitate conversion of the first resistfilm to be alkali soluble and crosslinking reaction to impart resistanceto organic solvent used in coating of the second resist film, anappropriate temperature is at least 150° C., and more preferably in therange of 180 to 220° C. In general, a photoacid generator and basiccompound in a resist composition serve as plasticizers, with thetendency that the resist pattern has a lower Tg and thermal flow beginsat a lower temperature. Since the photoacid generator and basic compoundare essential for the resist composition, it is necessary to select abase resin having a high Tg while taking into account the plasticizingeffect by the addition of photoacid generator and basic compound. Anappropriate Tg of base resin is at least 150° C., and more preferably atleast 180° C. If the temperature reached by heating to inducecrosslinking reaction is higher than 220° C., then an optimum firstresist pattern for reversal transfer to the second resist cannot beobtained due to substantial thermal shrinkage or thermal damage to thefirst resist pattern. If the temperature reached by heating to inducecrosslinking reaction is lower than 150° C., then crosslinking reactionmay occur short.

Next, as shown in FIG. 5, state (D), the reversal film-formingcomposition or second resist composition is coated and built up until itcovers or overlies the crosslinked first resist pattern 30 b, forming areversal film (or second resist film) 40.

In another embodiment, the first resist pattern has an increased height,and the coating of the second resist film has a reduced thickness asshown in FIG. 6, state (D-1). Then the first resist pattern which hasbeen converted to be soluble in alkaline developer may be exposed to analkaline developer whereby the first resist pattern may be removed fromthe second resist film serving as the reversal transfer film.

In the embodiment shown in FIG. 5, state (D), the second resist film(serving as the reversal transfer film) overlying the first resistpattern must be removed so that the first resist pattern which has beenconverted (or reversed) to be soluble in alkaline developer may becontacted with an alkaline developer. Then the second resist film(serving as the reversal transfer film) overlying the first resistpattern is previously converted to be somewhat soluble in alkalinedeveloper and then slimmed until the first resist pattern which has beenconverted to be soluble in alkaline developer is exposed to an alkalinedeveloper.

Where the second resist film (serving as the reversal transfer film)overlying the first resist pattern is removed until access is gained tothe first resist pattern which has been converted to be soluble inalkaline developer, this may be accomplished by a measure other than theabove-mentioned measure of endowing the second resist film (serving asthe reversal transfer film) with solubility in alkaline developer. Thealternative measure is as follows. In the step of heating at hightemperature to endow the first resist pattern with resistance to solventused in coating of the second resist film while keeping some acid whichhas diffused from the exposed area and remains in the first resistpattern or keeping the first resist pattern soluble in alkalinedeveloper, the photoacid generator remaining in the first resist patternfrom the resist composition is thermally decomposed to generate an acidwhich acts on alkali soluble groups protected with acid labile groupswhich are eliminatable with acid in the second resist film overlying thefirst resist pattern. Then, acid elimination occurs in the baking stepsinvolved in a process comprising the steps of coating, prebaking,exposing and post-exposure baking the second resist film, whereby thesecond resist film overlying the first resist pattern is converted to bealkali soluble. As a result, during development of the second resistfilm for patterning, the second resist film overlying the first resistpattern can also be dissolved away, and the reversed first resistpattern can be removed.

In the embodiment wherein the second resist film (serving as reversaltransfer film) overlying the reversed first resist pattern is removedsolely by heating at high temperature so that the first resist patternmay be dissolved in an alkaline developer, the coating thicknesses offirst and second resist films become crucial. Appropriate thicknesses offirst and second resist films to be coated are discussed below. Relativeto the thickness of a first resist film coated onto a flat substrate,the thickness of a second resist film coated onto a flat substrate ispreferably 60 to 50%. If the coating thickness of a second resist filmis thicker than the range, the second resist film overlying the firstresist pattern may not be fully converted to be alkali soluble, thesecond resist film may not be removed, an alkaline developer may notgain access to the first resist pattern, and reversal and removal of thefirst resist pattern may not be done. If the coating thicknesses are toothin, a double pattern obtained after patterning of the second resistincluding a pattern of reversal transfer of the first resist pattern maynot have a certain thickness.

FIG. 7 shows the state (E) that the reversed first resist pattern isdissolved away in an alkaline developer without patterning of the secondresist film serving as the reversal transfer film.

On the other hand, the first resist pattern which has been converted tobe soluble in alkaline developer ensures that reversal of the firstresist pattern and pattern formation of the second resist film takeplace simultaneously during the development step for patterning thesecond resist film.

The second resist film for reversal transfer coated on the first resistpattern is patterned by the same method as the first resist filmpatterning method. The method is the same as described for thepatterning of the first resist film.

Notably, the patterning of the second resist film may be performed byseveral modes which have their own advantage.

One mode is by effecting exposure to form a second resist pattern sothat spaces thereof (exposed area 50) are disposed between features ofthe reversed first resist pattern as shown in FIG. 8, state (F-1). Inthis case, the first resist pattern converted to be alkali soluble isdissolved away in an alkaline developer to leave spaces, and the secondresist pattern defines spaces therebetween. As a result, a doublepatterning process of forming closely packed lines and spaces becomespossible, FIG. 9, state (F-2).

Advantageously this double patterning process of forming a closelypacked line-and-space pattern has an ability to form lines and spaces ofa size which cannot be achieved by the single patterning process.

Another mode of exposure of the second resist film is by effectingexposure at a position spaced apart from the first resist pattern to bereversed into spaces as shown in FIG. 10, state (F-3).

In state (F-3) of FIG. 10, the first resist pattern is finished as thinlines as a result of over-exposure, and converted to be alkali solubleby heating at high temperature, whereby the pattern is finished as thin(or narrow) spaces. A patterning process of forming a very thin spacepattern and an isolated line pattern at the same time is very difficultbecause their characteristics are in trade-off relationship. The doublepatterning process of the invention succeeds in overcoming the trade-offbecause a very thin space pattern can be formed by reversal transfer ofthe first resist film and an isolated line pattern can be formed bypatterning the second resist film. The process is advantageous inprocessing a layer to form fine spaces and isolated lines in combinationas shown in FIG. 11, state (F-4).

A further mode is exposure of the second resist film to a cutout patterntransverse to the first resist pattern as shown in FIG. 12, step (G-1).By developing the exposed area 50 of the second resist film and thepositive/negative reversed first resist pattern, a crisscross cutoutpattern intersecting the second pattern in the form of trench patterncan be formed as shown in FIG. 13, state (G-2).

A still further mode is exposure of the second resist film to a remainline pattern perpendicular to the first resist pattern as shown in FIG.14, state (H-1). Since the second lines are interrupted by the firstpattern, a pattern of rectangular shaped dots at a fine pitch can beformed as shown in FIG. 15, state (H-2). This method results inrectangular holes, although a double dipole method generally forms a dotpattern consisting of circular shaped holes as shown in FIG. 17.

A still further mode involves double exposures of lines in X and Ydirections as shown in FIG. 16, state (I-1), and subsequent developmentto form a dot pattern as shown in FIG. 17, state (I-2). A second resistcomposition is coated thereon, exposed to a pattern of holes disposedbetween the dots, and developed. Development of the thus exposed secondresist film facilitates positive/negative reversal of the first patternfrom the dot pattern to a hole pattern, which is resolved at the sametime as holes of the second pattern as shown in FIG. 18, state (I-3). InFIG. 16, 30 c is an exposed area resist pattern.

For exposure of the second resist, high-energy radiation having awavelength of up to 300 nm is preferably used. Examples of suchradiation include a KrF excimer laser with a wavelength of 248 nm, anArF excimer laser of 193 nm, a F₂ laser of 157 nm, EB, EUV, and x-ray.Of these, the ArF excimer laser of 193 nm is preferably used. Theexposure from the ArF excimer laser may be either immersion lithographyusing water or dry lithography, with the immersion lithography beingpreferred for forming finer size patterns. In the ArF excimer laserlithography, materials having aromatic rings (exclusive of naphthalenerings) cannot be used as the base polymer, and instead, methacrylatesand other materials having a cyclic structure are preferably used. WhereKrF excimer laser, EB or EUV lithography is applied, materials havingaromatic rings like phenol groups may be used.

When it is desired to form fine holes between features of the firstresist pattern using the second resist serving as image reversal film,as shown in FIGS. 16 to 18, the use of ArF excimer laser or EBlithography is preferred because a very high resolution capability isrequired.

Furthermore, using the reversed pattern 40 a as a mask, the intermediateintervening layer of hard mask or the like (if any) may be etched, andthe processable substrate 20 further etched. For etching of theintermediate intervening layer of hard mask or the like, dry etchingwith fluorocarbon or halogen gases may be used. For etching of theprocessable substrate, the etching gas and conditions may be properlychosen so as to establish an etching selectivity relative to the hardmask, and specifically, dry etching with fluorocarbon, halogen, oxygen,hydrogen or similar gases may be used. Thereafter, the crosslinkedresist film and second resist film are removed. Removal of these filmsmay be carried out after etching of the intermediate intervening layerof hard mask or the like. It is noted that removal of the crosslinkedresist film may be achieved by dry etching with oxygen or radicals andremoval of the second resist film may be achieved as previouslydescribed, or using strippers such as amines, sulfuric acid/aqueoushydrogen peroxide or organic solvents.

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation. The abbreviations used herein are GPC for gelpermeation chromatography, Mw for weight average molecular weight, Mnfor number average molecular weight, Mw/Mn for molecular weightdistribution or dispersity, NMR for nuclear magnetic resonance, PAG forphotoacid generator, TAG for thermal acid generator, Me for methyl, andEt for ethyl. For all polymers, Mw and Mn are determined by GPC versuspolystyrene standards.

Synthesis Example 1

Polymers for use in first resist compositions for reversal and secondresist compositions subject to reversal transfer of first resist filmwere prepared by combining various monomers, effecting copolymerizationreaction in tetrahydrofuran medium, crystallization in methanol,repeatedly washing with hexane, isolation, and drying. The resultingpolymers (Resist Polymers 1 to 9 and Comparative Resist Polymers 10 to12) had the composition shown below. Notably, a phenol group on amonomer was substituted by an acetoxy group, which was converted back toa phenol group by alkaline hydrolysis after polymerization. Thecomposition of each polymer was analyzed by ¹H-NMR, and the Mw and Mw/Mndetermined by GPC.

Resist Polymer 1

(polymer for use in first resist composition)

-   -   Mw=8,300    -   Mw/Mn=1.73

Resist Polymer 2

(polymer for use in first resist composition)

-   -   Mw=7,300    -   Mw/Mn=1.67

Resist Polymer 3

(polymer for use in first and second resist compositions)

-   -   Mw=7,700    -   Mw/Mn=1.68

Resist Polymer 4

(polymer for use in first resist composition)

-   -   Mw=7,500    -   Mw/Mn=1.67

Resist Polymer 5

(polymer for use in first resist composition)

-   -   Mw=8,000    -   Mw/Mn=1.71

Resist Polymer 6

(polymer for use in first resist composition)

-   -   Mw=6,700    -   Mw/Mn=1.67

Resist Polymer 7

(polymer for use in first resist composition)

-   -   Mw=7,800    -   Mw/Mn=1.66

Resist Polymer 8

(polymer for use in second resist composition)

-   -   Mw=7,900    -   Mw/Mn=1.67

Resist Polymer 9

(polymer for use in second resist composition)

-   -   Mw=7,400    -   Mw/Mn=1.63

Comparative Resist Polymer 10

(comparative polymer for use in first resist composition)

-   -   Mw=7,700    -   Mw/Mn=1.68

Comparative Resist Polymer 11

(comparative polymer for use in first resist composition)

-   -   Mw=6,600    -   Mw/Mn=1.67

Comparative Resist Polymer 12

(comparative polymer for use in first resist composition)

-   -   Mw=7,500    -   Mw/Mn=1.80

Polysiloxanes for use in second resist compositions for reversaltransfer were synthesized as follows.

Synthesis Example 2

A 200-ml four-neck flask equipped with a stirrer, reflux condenser,dropping funnel, and thermometer was charged with 0.2 g of acetic acid,20 g of water and 20 g of ethanol and kept at 30° C. To the flask, asolution of 10.8 g (30 mmol) of triethoxysilane compound A, 8.8 g (20mmol) of triethoxysilane compound B, and 16.4 g (50 mmol) oftriethoxysilane compound C in 40 g of ethanol was added dropwise over 3hours.

The reaction mixture was aged at 30° C. for a further 20 hours, dilutedwith methyl isobutyl ketone, repeatedly washed with water until theorganic layer became neutral, and concentrated, yielding 27.6 g of anoligomer.

Using 50 g of toluene, the oligomer was transferred into a 100-mlthree-neck flask equipped with a stirrer, reflux condenser, andthermometer. Then 56 mg of potassium hydroxide was added to thesolution, which was heated under reflux for 20 hours. The reactionsolution was cooled, diluted with methyl isobutyl ketone, repeatedlywashed with water until the organic layer became neutral, andconcentrated, yielding 24.9 g of a polymer.

On NMR and GPC analysis, the product was identified to be Resist Polymer13 of the following compositional formula, having a Mw of 3,500.

Resist Polymer 13

(polysiloxane for use in second resist composition)

-   -   Mw=3,500

Variants of the ethoxysilane compound of the structure shown above couldbe formed by changing the silicon-bonded substituent structure.Thereafter, using these ethoxysilane variants, polysiloxane compounds ofdifferent constituent units, designated Resist Polymers 14 and 15, weresynthesized by the same procedure as the above synthesis example.

Resist Polymer 14

(polysiloxane for use in second resist composition)

-   -   Mw=3,600

Resist Polymer 15

(polysiloxane for use in second resist composition)

-   -   Mw=2,000

Resist Polymer 16

(phenolic polymer for use in second resist composition)

-   -   Mw=6,000

Resist Polymer 17

(phenolic polymer for use in second resist composition)

-   -   Mw=7,400

Resist Polymer 18

(phenolic polymer for use in second resist composition)

-   -   Mw=6,300

Resist Polymer 19

(phenolic polymer for use in second resist composition)

-   -   Mw=6,600

Resist Polymer 20

(phenolic polymer for use in second resist composition)

-   -   Mw=6,600

Example And Comparative Example

The polymers synthesized above were combined with a photoacid generator,basic compound, surfactant, thermal acid generator, surface dissolutionrate improver (Surface DRR), and organic solvent. To 100 parts of theorganic solvent was added 0.005 parts of surfactant FC-4430 (Sumitomo 3MCo., Ltd.). The ingredients were thoroughly mixed to form resistcompositions.

-   Acid generator: PAG1, 2 of the following structural formula

-   Basic compound: Quencher 1 to 3 of the following structural formula

Thermal Acid Generator:

-   -   TAG1 of the following structural formula

Surface Dissolution Rate Improver:

-   -   Surface DRR of the following structural formula

Organic Solvent: Propylene Glycol Monomethyl Ether Acetate (PGMEA)

Table 1 tabulates the formulation of first resist composition, secondresist composition and comparative first resist composition.

TABLE 1 Resist Formulation Polymer PAG Basic compound TAG Solventcomposition No. (pbw) (pbw) (pbw) (pbw) (pbw) 1st resist I-001 ResistPolymer 1 PAG1 Quencher 1 — PGMEA (100) (16) (3) (2,700) 1st resistI-002 Resist Polymer 2 PAG1 Quencher 1 — PGMEA (100) (16) (3) (2,700)1st resist I-003 Resist Polymer 3 PAG1 Quencher 1 — PGMEA (100) (16) (3)(2,700) 1st resist I-004 Resist Polymer 4 PAG1 Quencher 1 — PGMEA (100)(16) (3) (2,700) 1st resist I-005 Resist Polymer 4 PAG1 Quencher 1 TAG1PGMEA (100) (16) (3) (0.5) (2,700) 1st resist I-006 Resist Polymer 5PAG1 Quencher 1 — PGMEA (100) (16) (3) (2,700) 1st resist I-007 ResistPolymer 6 PAG1 Quencher 1 — PGMEA (100) (16) (3) (2,700) 1st resistI-008 Resist Polymer 7 PAG1 Quencher 1 — PGMEA (100) (16) (3) (2,700)Comparative I-009 Resist Polymer 10 PAG1 Quencher 1 — PGMEA 1st resist(100) (16) (3) (2,700) Comparative I-010 Resist Polymer 11 PAG1 Quencher1 — PGMEA 1st resist (100) (16) (3) (2,700) Comparative I-011 ResistPolymer 12 PAG1 Quencher 1 — PGMEA 1st resist (100) (16) (3) (2,700) 2ndresist II-001 Resist Polymer 3 PAG1 Quencher 1 — PGMEA (100) (16) (7)(5,000) 2nd resist II-002 Resist Polymer 8 PAG1 Quencher 1 — PGMEA (100)(16) (7) (5,000) 2nd resist II-003 Resist Polymer 9 PAG1 Quencher 1 —PGMEA  (93) (16) (7) (5,000) Surface DRR  (7) 2nd resist II-004 ResistPolymer 13 PAG1 Quencher 2 — PGMEA (100)  (6) (1) (3,500) 2nd resistII-005 Resist Polymer 14 PAG1 Quencher 2 — PGMEA (100)  (6) (1) (3,500)2nd resist II-006 Resist Polymer 15 PAG1 Quencher 2 — PGMEA (100)  (6)(1) (3,500) 2nd resist II-007 Resist Polymer 16 PAG2 Quencher 3 — PGMEA(100)  (8)   (1.5) (3,500) 2nd resist II-008 Resist Polymer 17 PAG2Quencher 3 — PGMEA (100)  (8)   (1.5) (3,500) 2nd resist II-009 ResistPolymer 18 PAG2 Quencher 3 — PGMEA (100)  (8)   (1.5) (3,500) 2nd resistII-010 Resist Polymer 19 PAG2 Quencher 3 — PGMEA (100)  (8)   (1.5)(3,500) 2nd resist II-011 Resist Polymer 20 PAG2 Quencher 3 — PGMEA(100)  (8)   (1.5) (3,500)

Table 2 tabulates the first resist patterning data of Examples 1 to 8and Comparative Examples 1 to 3.

The resist compositions prepared according to the formulation shown inTable 1 were filtered through a tetrafluoroethylene filter having a poresize of 0.2 μm, yielding positive resist film-forming coating solutions.

On a substrate (silicon wafer) having deposited thereon anantireflective coating (ARC-29A, Nissan Chemical Industries, Ltd.) of 90nm thick, each of the resist compositions was spin coated and prebakedon a hot plate at an optimum temperature for 60 seconds to form a resistfilm of 1,200 Å thick. As used herein, the term “optimum temperature”refers to the prebaking temperature which ensures that a patternresulting from subsequent processing has a satisfactory profile which ishighly rectangular and free of bridges or pattern edge chipping, whenobserved under top-down scanning electron microscope (TDSEM) S9320(Hitachi, Ltd.). The optimum prebaking temperature is shown in Table 2.

The first resist film thus formed was subjected to pattern exposure bymeans of an ArF excimer laser scanner S-307E (Nikon Corp., NA 0.85, σ0.93-0.62, dipole illumination). The mask used was a 6% halftone phaseshift mask (HTPSM) bearing thereon a line-and-space design consisting of70-nm lines and 160-nm pitches (equivalent resist pattern size).Exposure of the resist film was done while selecting an optimum focusand varying the exposure dose from a minimum dose to a maximum dose.

Following exposure, the resist film was baked on a hot plate(post-exposure bake, PEB). The appropriate PEB temperature for eachresist composition is also reported in Table 2. The appropriate PEBtemperature refers to the temperature at which a wide process margin isobserved for that resist composition. PEB for 60 seconds was followed bydevelopment in a 2.38 wt % tetramethylammonium hydroxide (TMAH) aqueoussolution for 30 seconds, yielding a positive pattern.

Table 2 reports the optimum exposure dose at which 40-nm lines werefinished from the line-and-space design consisting of 70-nm lines and160-nm pitches (equivalent resist pattern size) on the mask.

Now, to convert the first resist film to be alkali soluble and to impartthereto resistance to solvent for a second resist film to which thefirst resist pattern is to be transferred, the first resist film washeated at a high temperature. This heating was done on a hot plate at atemperature of 200° C. for 60 seconds. After this heating, a change inthe size of 40-nm lines finished as above was measured. Table 2 reportsthe line size after heating.

TABLE 2 Optimum exposure dose capable of 40 nm finish from mask Linesize after 1st resist Prebaking PEB design of 70 nm 200° C. × 60 secformulation temperature temperature line/160 nm pitch heating No. (° C.× 60 sec) (° C. × 60 sec) (mJ) (nm) Example 1 I-001 100 100 50 37Example 2 I-002 100 90 52 39 Example 3 I-003 100 90 52 38 Example 4I-004 115 110 47 38 Example 5 I-005 115 110 43 39 Example 6 I-006 105 9553 38 Example 7 I-007 100 100 45 38 Example 8 I-008 100 100 45 37Comparative I-009 100 100 50 45 Example 1 Comparative I-010 100 100 5043 Example 2 Comparative I-011 95 90 50 52 Example 3

In Comparative Example 3, the 40 nm lines after patterning were changedto be thicker by 200° C.×60 sec heating. A thermal flow was observed inthe first resist pattern of Comparative Example 3 because the resistcomposition had a low glass transition temperature (Tg). The resistcomposition of Comparative Example 3 is inadequate because of a failureof nano-scale patterning of the first resist as reversal transferpattern.

Next, a second resist composition was coated onto the first resistpattern obtained in Examples 1 to 8 and Comparative Examples 1 and 2.The coating thickness of the second resist composition was set at 600 Åon a flat substrate. Table 3 shows a change of the first resist patternwhen the second resist composition was coated thereon. The prebakingtemperature in coating of the second resist composition is also reportedin Table 3.

TABLE 3 2nd resist coating 2nd resist thickness 2nd resist prebaking onflat 1st resist pattern 1st resist formulation temperature substrateafter pattern No. (° C. × 60 sec) (Å) 2nd resist coating Example 9pattern of II-001 100 600 2nd resist was properly Example 1 coated on1st resist Example 10 pattern of II-001 100 600 2nd resist was properlyExample 2 coated on 1st resist Example 11 pattern of II-001 100 600 2ndresist was properly Example 3 coated on 1st resist Example 12 pattern ofII-001 100 600 2nd resist was properly Example 4 coated on 1st resistExample 13 pattern of II-001 100 600 2nd resist was properly Example 5coated on 1st resist Example 14 pattern of II-001 100 600 2nd resist wasproperly Example 6 coated on 1st resist Example 15 pattern of II-001 100600 2nd resist was properly Example 7 coated on 1st resist Example 16pattern of II-001 100 600 2nd resist was properly Example 8 coated on1st resist Comparative pattern of II-001 100 600 1st resist wasdissolved Example 4 Comparative in 2nd resist solution, Example 1pattern was disrupted Comparative pattern of II-001 100 600 1st resistwas dissolved Example 5 Comparative in 2nd resist solution, Example 2pattern was disrupted

In Comparative Examples 4 and 5, the first resist pattern was disruptedby attack of the solvent in the second resist composition. Since thepolymers in the first resist compositions of Comparative Examples 4 and5 were not crosslinked during the high-temperature heating step forimparting organic solvent resistance, they were dissolved in the secondresist solvent.

Next, a second resist composition was coated onto the first resistpattern obtained in Examples 1 to 8 as above. The second resist filmthus coated was directly (without pattern exposure) baked (PEB) at atemperature for the second resist film and then developed with a 2.38 wt% TMAH solution for 30 seconds. Since the first resist pattern had beenconverted alkali soluble, its pattern was reversal transferred to thesecond resist film. This was observed under TDSEM S9320 (Hitachi, Ltd.).In addition the size of the pattern which was reversal transferred tothe second resist film was measured. The results are shown in Table 4.

In a comparative example, coatings of the second resist compositionhaving varying thickness were formed and the patterns of the secondresist film after reversal transfer were observed. The results are shownin Table 4. If the second resist film is thick, the alkaline developermay not readily gain access to the first resist film which has beenconverted to be alkali soluble, causing transfer failure.

TABLE 4 2nd resist Pattern (space) Pattern (space) 2nd coating 2ndreversal reversal 2nd resist thickness resist transferred to transferredto 1st resist prebaking on flat PEB 2nd resist 2nd resist resistformulation temperature substrate temperature film, film, pattern No. (°C. × 60 sec) (Å) (° C. × 60 sec) TDSEM profile size (nm) Example 17pattern of II-001 100 600 90 good 30 Example 1 Example 18 pattern ofII-001 100 600 90 good 32 Example 2 Example 19 pattern of II-001 100 60090 good 31 Example 3 Example 20 pattern of II-001 100 600 90 good 33Example 4 Example 21 pattern of II-001 100 600 90 good 33 Example 5Example 22 pattern of II-001 100 600 90 good 35 Example 6 Example 23pattern of II-001 100 600 90 good 32 Example 7 Example 24 pattern ofII-001 100 600 90 good 36 Example 8 Example 25 pattern of II-002 100 600100 good 33 Example 4 Example 26 pattern of II-003 100 600 100 good 31Example 4 Example 27 pattern of II-004 120 600 100 good 30 Example 4Example 28 pattern of II-005 120 600 100 good 32 Example 4 Example 29pattern of II-006 120 600 100 good 33 Example 4 Comparative pattern ofII-001 120 700 100 bridges in — Example 6 Example 4 spaces of reversaltransferred pattern, spaces not fully open Comparative pattern of II-001120 800 100 spaces almost — Example 7 Example 4 closed Comparativepattern of II-001 120 900 100 even trace of — Example 8 Example 4reversal pattern not observed

Next, on the first resist pattern which had been converted (or reversed)to be soluble in alkaline developer, a second resist film was formed andexposed under the following conditions so as to define a pattern ofspaces between features of the first resist pattern. Pattern exposurewas carried out by means of an ArF scanner S-307E (Nikon Corp., NA 0.85,σ 0.93-0.62, dipole illumination). The mask used was a 6% halftone phaseshift mask (HTPSM) bearing thereon a line-and-space design consisting of70-nm lines and 160-nm pitches (equivalent resist pattern size).Exposure of the second resist film was done while selecting an optimumfocus and varying the exposure dose from a minimum dose to a maximumdose. The same mask as used in exposure of the first resist film wasused at this stage, because the line pattern in the unexposed area ofthe first resist was reversed into a space pattern and its positionoverlapped the line pattern in the unexposed area of second resistpattern exposure, and so the same line-and-space arrangement might beused. Since the mask bears thereon a line-and-space design consisting of70-nm lines and 160-nm pitches (or 90-nm spaces), a second resist spacepattern of 40 nm could be resolved at a low exposure dose. The spacepattern size resulting from reversal transfer of the first resist wasintended to be 40 nm. This succeeded in a double patterning processcapable of forming repeat patterns of 40-nm lines (and spaces) and 80-nmpitches. The results are shown in Table 5. Table 5 also reports theexposure dose of resolving the second resist to 40 nm and the profilefollowing double patterning.

TABLE 5 Optimum exposure for space 2nd 40 nm finish resist from 2ndcoating 2nd 2nd resist 2nd resist thickness resist mask design Profile1st resist prebaking on flat PEB of after resist formulation temperaturesubstrate temperature 70 nm line/ double pattern No. (° C. × 60 sec) (Å)(° C. × 60 sec) 160 nm pitch patterning Example 30 pattern of II-001 100600 90 32 some top loss Example 1 Example 31 pattern of II-001 100 60090 32 some top loss Example 2 Example 32 pattern of II-001 100 600 90 32some top loss Example 3 Example 33 pattern of II-001 100 600 90 32 sometop loss Example 4 Example 34 pattern of II-001 100 600 90 32 some toploss Example 5 Example 35 pattern of II-001 100 600 90 32 some top lossExample 6 Example 36 pattern of II-001 100 600 90 32 some top lossExample 7 Example 37 pattern of II-001 100 600 90 32 some top lossExample 8 Example 38 pattern of II-002 100 600 100 32 rounded Example 4Example 39 pattern of II-003 100 600 100 30 rectangular, Example 4 goodExample 40 pattern of II-004 120 600 100 30 some top loss Example 4Example 41 pattern of II-005 120 600 100 28 rectangular, Example 4 goodExample 42 pattern of II-006 120 600 100 28 rectangular, Example 4 good

On a silicon wafer, an undercoat material ODL-50 (Shin-Etsu ChemicalCo., Ltd.) was coated and baked on a hot plate at 250° C. for 60 secondsto form an undercoat of 200 nm thick (carbon content 80 wt %). Asilicon-containing intermediate film material SHB-A940 (Shin-EtsuChemical Co., Ltd.) was coated thereon and baked at 200° C. for 60seconds to form a silicon-containing intermediate film of 35 nm thick(silicon content 43 wt %). A photoresist composition was coated thereonand prebaked at 100° C. for 60 seconds to form a first photoresist filmof 120 nm thick.

The first resist film thus formed was exposed to a pattern of five Ydirection lines having a width of 70 nm, a pitch of 140 nm and a lengthof 700 nm by means of an ArF excimer laser scanner S-307E (Nikon Corp.,NA 0.85, σ 0.93-0.62, dipole illumination for Y-direction lines) througha 6% halftone phase shift mask. Following exposure, the film was baked(PEB) at 100° C. for 60 seconds and developed with a 2.38 wt % TMAHsolution for 30 seconds. A pattern of 70 nm lines in Y direction wasformed and then baked at 190° C. for 60 seconds to induce crosslinkingand deprotection. The line width of the first resist pattern wasmeasured.

In Example 43, a second resist composition was coated on the first linepattern to form a second resist film of 50 nm thick. To define a singleX-direction line intersecting perpendicularly the first pattern, thesecond resist film was exposed to a trench pattern having a line widthof 150 nm and a length of 1 μm by means of an ArF excimer laser scannerS-307E (Nikon Corp., NA 0.85, σ 0.93-0.62, annular illumination) througha 6% halftone phase shift mask. This was followed by baking at 100° C.for 60 seconds and development in a 2.38 wt % TMAH solution for 30seconds, yielding a X-direction trench pattern having a width of 150 nmintersecting the five Y-direction 70 nm trenches.

In Example 44, a second resist composition was coated on the first linepattern to form a second resist film of 60 nm thick. To define a singleX-direction line intersecting perpendicularly the first pattern, thesecond resist film was exposed to a trench pattern having a line widthof 200 nm and a length of 1 μm by means of a KrF excimer laser scannerS-203B (Nikon Corp., NA 0.68, σ 0.75-0.50, annular illumination) througha 6% halftone phase shift mask. This was followed by baking at 100° C.for 60 seconds and development in a 2.38 wt % TMAH solution for 30seconds, yielding a X-direction trench pattern having a width of 200 nmintersecting the five Y-direction 70 nm trenches.

In Comparative Example 9, the resist film was exposed by means of an ArFexcimer laser scanner S-307E (Nikon Corp., NA 0.85, σ 0.93-0.62,cross-pole illumination) through a 6% halftone phase shift mask having a150 nm X-direction trench pattern (calculated as on-wafer size)overlapping a pattern of five Y-direction 70 nm lines at 140 nm pitches,as shown in FIG. 19 (consisting of a shifter light-shielding region ingrey zone G and a light-transmissive region in white zone W). This wasfollowed by baking at 100° C. for 60 seconds and development in a 2.38wt % TMAH solution for 30 seconds, yielding a 150 nm wide X-directiontrench pattern intersecting the five Y-direction 70 nm trenches.

The size of the line pattern of first resist Y-direction lines and thespace width measurement size of Y-direction spaces after second resistdevelopment and subsequent reversal, the size of X-direction trenches ofsecond resist pattern, and the profile at the intersection between thesecond pattern and the first pattern were observed under SEM. Theresults are shown in Table 6.

FIG. 19 shows the resist pattern obtained in Examples 43 and 44, andFIG. 20 shows the resist pattern obtained in Comparative Example 9. Thegrey zone G designates the region where the resist is retained, and thewhite zone W designates the region where the resist has been dissolvedaway.

TABLE 6 1st resist 1st 2nd pattern Shape of 1st 2nd resist resist sizeintersection resist resist pattern pattern after between formulationformulation size size reversal 1st and 2nd No. No. (nm) (nm) (nm)patterns Example 43 I-001 II-001 70 150 72 perpendicular Example 44I-001 II-007 70 200 73 perpendicular Comparative I-001 — 70 150 72rounded Example 9

On a silicon wafer, an undercoat material ODL-50 (Shin-Etsu ChemicalCo., Ltd.) was coated and baked on a hot plate at 250° C. for 60 secondsto form an undercoat of 200 nm thick. A silicon-containing intermediatefilm material SHB-A940 (Shin-Etsu Chemical Co., Ltd.) was coated thereonand baked at 200° C. for 60 seconds to form a silicon-containingintermediate film of 35 nm thick. A photoresist composition was coatedthereon and prebaked at 100° C. for 60 seconds to form a firstphotoresist film of 120 nm thick.

The first resist film thus formed was exposed to a pattern of fiveY-direction lines having a width of 70 nm, a pitch of 140 nm and alength of 700 nm by means of an ArF excimer laser scanner S-307E (NikonCorp., NA 0.85, σ 0.93-0.62, dipole illumination for Y direction lines)through a 6% halftone phase shift mask. Following exposure, the film wasbaked (PEB) at 100° C. for 60 seconds and developed with a 2.38 wt %TMAH solution for 30 seconds. A pattern of 70 nm lines in Y directionwas formed and then baked at 190° C. for 60 seconds to inducecrosslinking and deprotection. The line width of the first resistpattern was measured.

In Example 45, a second resist composition was coated on the first linepattern to form a second resist film of 50 nm thick. To define fiveX-direction lines intersecting perpendicularly the first pattern, thesecond resist film was exposed to a pattern of 5 X-direction lineshaving a line width of 70 nm, a pitch of 140 nm and a length of 700 nmby means of an ArF excimer laser scanner S-307E (Nikon Corp., NA 0.85, σ0.93-0.62, dipole illumination for X direction lines) through a 6%halftone phase shift mask. This was followed by baking at 100° C. for 60seconds and development in a 2.38 wt % TMAH solution for 30 seconds,yielding a dot pattern resulting from five X-direction lines andpositive/negative reversal of overlapping Y-direction lines.

In Comparative Example 10, the resist film was exposed through a mask ofthe shape shown in FIG. 21 including five X-direction 70 nm lines at 140nm pitches (on-mask size) and 70 nm dots. This was followed by baking at100° C. for 60 seconds and development in a 2.38 wt % TMAH solution for30 seconds, yielding a dot pattern formed from five X-direction 70 nmlines and 70 nm dots.

The size of lines and dots after development was measured under SEM. Theresults are shown in Table 7.

FIG. 21 shows the resist pattern after development in Example 45, andFIG. 22 shows the resist pattern after development in ComparativeExample 10.

TABLE 7 1st 1st resist 2nd resist resist Resist formulation formulationline size dot size No. No. (nm) (nm) Dot shape Example 45 I-001 II-00170 68 perpen- dicular Comparative I-001 — 70 20 rounded Example 10

On a silicon wafer, an undercoat material ODL-50 (Shin-Etsu ChemicalCo., Ltd.) was coated and baked on a hot plate at 250° C. for 60 secondsto form an undercoat of 200 nm thick. A silicon-containing intermediatefilm material SHB-A940 (Shin-Etsu Chemical Co., Ltd.) was coated thereonand baked at 200° C. for 60 seconds to form a silicon-containingintermediate film of 35 nm thick. A photoresist composition was coatedthereon and prebaked at 100° C. for 60 seconds to form a firstphotoresist film of 120 nm thick.

The first resist film thus formed was exposed by means of an ArF excimerlaser scanner S-307E (Nikon Corp., NA 0.85, σ 0.93-0.62) through a 6%halftone phase shift mask to a pattern of Y-direction lines having aline width of 70 nm and a pitch of 140 nm under Y direction dipoleillumination and then to a pattern of X-direction lines having a widthof 70 nm at a pitch of 140 nm under X direction dipole illumination.Following exposure, the film was baked (PEB) at 100° C. for 60 secondsand developed with a 2.38 wt % TMAH solution for 30 seconds. A patternof dots having a size of 50 nm and a pitch of 140 nm was formed and thenbaked at 190° C. for 60 seconds to induce crosslinking and deprotection.

A second resist composition was coated on the dot pattern and prebakedat 100° C. for 60 seconds to form a second photoresist film of 60 nmthick. Using an EB writing system HL-800D (Hitachi, Ltd.) at a HVvoltage of 50 keV, a hole pattern was written between dots of the firstresist pattern in a vacuum chamber.

Exposure was followed by baking at 100° C. for 60 seconds anddevelopment in a 2.38 wt % TMAH solution for 30 seconds. The firstresist dot pattern was converted into a hole pattern throughpositive/negative reversal, and the second resist pattern was resolvedas a hole pattern.

The size of holes after development was measured under SEM. The resultsare shown in Table 8.

FIG. 18 shows the resist pattern after development in Examples 46 to 49.

TABLE 8 Hole size Hole size resulting resulting from from 1st resist 2ndresist reversal of exposure of formulation formulation 1st resist 2ndresist No. No. (nm) (nm) Example 46 I-001 II-008 51 65 Example 47 I-001II-009 52 60 Example 48 I-001 II-010 53 62 Example 49 I-001 II-011 52 63

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention.Therefore, it is intended that the invention not be limited to theparticular embodiment disclosed as the best mode contemplated forcarrying out this invention, but that the invention will include allembodiments falling within the scope of the appended claims.

Japanese Patent Application No. 2008-032668 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

The invention claimed is:
 1. A double pattern forming process comprisingthe steps of: coating a first chemically amplified positive resistcomposition onto a processable substrate, said resist compositioncomprising a resist polymer comprising recurring units having analkali-soluble group protected with an acid labile group which iseliminatable with acid, a photoacid generator capable of generating anacid upon exposure to high-energy radiation, and an organic solvent, andprebaking the resist composition to remove the solvent to form a resistfilm, exposing the resist film to high-energy radiation in a firstpattern of exposed and unexposed areas, post-exposure baking for causingthe acid generated by the acid generator upon exposure to act on theacid labile groups on the resist polymer whereby the acid labile groupson the resist polymer in the exposed area undergo elimination reactionso that the resist polymer in the exposed area becomes alkali soluble,and developing the exposed resist film with an alkaline developer toform a first positive resist pattern, treating the first resist patternso as to eliminate the acid labile groups on the resist polymer in thefirst resist pattern and to induce crosslinking in the resist polymer tosuch an extent that the resist polymer does not lose solubility in analkaline developer, for thereby endowing the first resist pattern withresistance to an organic solvent to be used in a reversal film-formingcomposition, coating a reversal film-forming composition thereon to forma reversal film, said reversal film-forming composition being a secondchemically amplified positive resist composition comprising a resistpolymer comprising recurring units having an alkali-soluble groupprotected with an acid labile group which is eliminatable with acid, aphotoacid generator capable of generating an acid upon exposure tohigh-energy radiation, and an organic solvent, and prebaking the secondresist composition to remove the solvent to form the reversal film, andexposing the reversal film to high-energy radiation in a second patternof exposed and unexposed areas, post-exposure baking for causing theacid generated by the acid generator upon exposure to act on the acidlabile groups on the resist polymer whereby the acid labile groups onthe resist polymer in the exposed area undergo elimination reaction, anddeveloping the exposed reversal film with an alkaline developer to forma second positive resist pattern, wherein the last step of developingthe exposed reversal film with an alkaline developer to form a secondresist pattern includes dissolving away the first resist pattern whichhas been converted to be soluble in the alkaline developer and achievingreversal transfer of the first resist pattern to the second resistpattern.
 2. The process of claim 1 wherein in the step of exposing,baking and developing to form a second resist pattern, exposure to thesecond pattern is performed between features of the first pattern todefine the second resist pattern of spaces which are removable byalkaline development and located between spaces in the pattern resultingfrom reversal transfer of the first resist pattern, whereby repetitivepatterns of lines and spaces are formed on the processable substrate. 3.The process of claim 1 wherein in the step of exposing, baking anddeveloping to form a second resist pattern, exposure to the secondpattern is performed at a position spaced apart from the first resistpattern, whereby the second resist pattern is formed on the processablesubstrate apart from the pattern resulting from reversal transfer of thefirst resist pattern.
 4. The process of claim 1 wherein in the step ofexposing, baking and developing to form a second resist pattern,exposure is performed to the second pattern that intersects the firstresist pattern, whereby a second space pattern is formed as intersectinga space pattern resulting from reversal transfer of the first resistpattern.
 5. The process of claim 1 wherein in the step of exposing,baking and developing to form a second resist pattern, exposure isperformed to the second pattern that intersects the first resistpattern, whereby a space pattern resulting from reversal transfer of thefirst resist pattern is formed in the second resist pattern.
 6. Theprocess of claim 1 wherein the step of exposure to a first pattern anddevelopment forms a first dot pattern, and the step of exposure to asecond pattern and development to form a second resist pattern includesexposure to a hole pattern between dots of the first dot pattern, anddevelopment to form a hole pattern between holes of a hole patternresulting from reversal transfer of the first dot pattern.
 7. Theprocess of claim 1 wherein in said first chemically amplified positiveresist composition, the resist polymer comprises recurring units havinga lactone ring and recurring units of alicyclic structure having analkali-soluble group protected with an acid labile group which iseliminatable with acid.
 8. The process of claim 7 wherein in said firstchemically amplified positive resist composition, the resist polymercomprises recurring units having a 7-oxanorbornane ring and recurringunits having an alkali-soluble group protected with an acid labile groupof alicyclic structure which is eliminatable with acid, and the step oftreating the first resist pattern so as to eliminate the acid labilegroups on the resist polymer in the first resist pattern is performed byheating whereby elimination of acid labile groups and crosslinking ofthe resist polymer simultaneously take place.
 9. The process of claim 7wherein in said first chemically amplified positive resist composition,the resist polymer comprises recurring units having the general formula(a):

wherein R¹ is hydrogen or methyl, R² is a single bond or a straight,branched or cyclic C₁-C₆ alkylene group which may have an ether or estergroup, and which has a primary or secondary carbon atom through which itis linked to the ester moiety in the formula, R³, R⁴, and R⁵ are eachindependently hydrogen or a straight, branched or cyclic C₁-C₆ alkylgroup, and “a” is a number in the range: 0<a<1.0.
 10. The process ofclaim 7 wherein the recurring units having an alkali-soluble groupprotected with an acid labile group which is eliminatable with acid arerecurring units having the general formula (b):

wherein R⁶ is hydrogen or methyl, R⁷ is an acid labile group, and b is anumber in the range: 0<b≦0.8.
 11. The process of claim 1 wherein in saidsecond chemically amplified positive resist composition, the resistpolymer comprises recurring units having a lactone ring and recurringunits having an alkali-soluble group protected with an acid labile groupwhich is eliminatable with acid.
 12. The process of claim 11 wherein insaid second chemically amplified positive resist composition, therecurring units having an alkali-soluble group protected with an acidlabile group which is eliminatable with acid are recurring units havingthe general formula (c):

wherein R⁸ is hydrogen or methyl, R⁹ is an acid labile group, and c is anumber in the range: 0<c≦0.8.
 13. The process of claim 1 wherein in saidsecond chemically amplified positive resist composition, the resistpolymer comprising recurring units having an alkali-soluble groupprotected with an acid labile group which is eliminatable with acid is apolysiloxane compound.
 14. The process of claim 13 wherein in saidsecond chemically amplified positive resist composition, thepolysiloxane compound comprises structural units having the generalformulae (1) and (2) and further comprises third structural units havingthe general formula (3):

wherein R¹⁰ is a C₃-C₂₀ monovalent organic group of straight, branched,cyclic or polycyclic structure which has a hydroxyl group on a carbonatom as a functional group, which has in total at least three fluorineatoms substituted on the carbon atoms bonded to the hydroxyl-bondedcarbon atom, and which may contain a halogen, oxygen or sulfur atom inaddition to the fluorine atoms, R¹¹ is a C₁-C₆ monovalent hydrocarbongroup of straight, branched or cyclic structure, R¹² is a C₃-C₂₀monovalent organic group of straight, branched, cyclic or polycyclicstructure which has a carboxyl group protected with an acid labileprotective group as a functional group, and which may contain a halogen,oxygen or sulfur atom in addition to the carboxyl group, R¹³ is asdefined for R¹¹, R¹⁴ is a C₄-C₁₆ monovalent organic group which has alactone ring as a functional group and which may contain a halogen,oxygen or sulfur atom in addition to the lactone ring, R¹⁵ is as definedfor R¹¹, p is 0 or 1, q is 0 or 1, and r is 0 or
 1. 15. The process ofclaim 1 wherein the step of treating the first resist pattern forendowing the first resist pattern with resistance to an organic solventto be used in a reversal film-forming composition includes heating at ahigher temperature than in the prebaking and PEB steps.
 16. A doublepattern forming process comprising the steps of: coating a firstchemically amplified positive resist composition onto a processablesubstrate, said resist composition comprising a resist polymercomprising recurring units having an alkali-soluble group protected withan acid labile group which is eliminatable with acid, a photoacidgenerator capable of generating an acid upon exposure to high-energyradiation, and an organic solvent, and prebaking the resist compositionto remove the solvent to form a resist film, coating a protectivefilm-forming composition onto the resist film and heating to removesolvent to form a protective film, exposing the resist film tohigh-energy radiation in a first pattern of exposed and unexposed areas,post-exposure baking for causing the acid generated by the acidgenerator upon exposure to act on the acid labile groups on the resistpolymer whereby the acid labile groups on the resist polymer in theexposed area undergo elimination reaction so that the resist polymer inthe exposed area becomes alkali soluble, and developing the exposedresist film with an alkaline developer to form a first positive resistpattern, treating the first resist pattern so as to eliminate the acidlabile groups on the resist polymer in the first resist pattern and toinduce crosslinking in the resist polymer to such an extent that theresist polymer does not lose solubility in an alkaline developer, forthereby endowing the first resist pattern with resistance to an organicsolvent to be used in a reversal film-forming composition, coating areversal film-forming composition thereon to form a reversal film, saidreversal film-forming composition being a second chemically amplifiedpositive resist composition comprising a resist polymer comprisingrecurring units having an alkali-soluble group protected with an acidlabile group which is eliminatable with acid, a photoacid generatorcapable of generating an acid upon exposure to high-energy radiation,and an organic solvent, and prebaking the second resist composition toremove the solvent to form the reversal film, coating a protectivefilm-forming composition onto the reversal film and heating to removesolvent to form a protective film, and exposing the reversal film tohigh-energy radiation in a second pattern of exposed and unexposedareas, post-exposure baking for causing the acid generated by the acidgenerator upon exposure to act on the acid labile groups on the resistpolymer whereby the acid labile groups on the resist polymer in theexposed area undergo elimination reaction, and developing the exposedreversal film with an alkaline developer to form a second positiveresist pattern, wherein the last step of developing the exposed reversalfilm with an alkaline developer to form a second resist pattern includesdissolving away the first resist pattern which has been converted to besoluble in the alkaline developer and achieving reversal transfer of thefirst resist pattern to the second resist pattern, thereby forming apattern resulting from reversal transfer of the first resist pattern andthe second resist pattern.